fix: memory over allocation due to last partial block group

[siddh34]

Description

This resolves issue #647

This is fix for memory over allocation due to last partial block

I have explicitly laid out metadata for extra/last groups

Modifications:

Packed-region math is computation starts at line 718

function to calculate blocks in last group at line 58

while loop here didn't made any sense so replaced it with if check line 914

[dkovba]

Thank you for the contribution!
Below are the test results across the size/content matrix, cross-checked with e2fsck:

Requested Size: 32KiB
Content: none
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 64MiB
Content: none
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 128MiB
Content: none
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 128MiB+4KiB
Content: none
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 130MiB+8KiB
Content: none
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 160MiB
Content: none
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 256MiB
Content: none
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 1GiB
Content: none
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 4GiB
Content: none
Size: FAIL
allocatedMiB <= ceilingMiB = false; allocatedMiB = 65; ceilingMiB = 32
e2fsck: PASS
----------------------------------------
Requested Size: 63x128MiB
Content: none
Size: FAIL
allocatedMiB <= ceilingMiB = false; allocatedMiB = 127; ceilingMiB = 32
e2fsck: PASS
----------------------------------------
Requested Size: 63x128MiB+4KiB
Content: none
Size: FAIL
allocatedMiB <= ceilingMiB = false; allocatedMiB = 129; ceilingMiB = 32
e2fsck: FAIL rc=4
Block bitmap differences:  +(32768--32930)
Fix? no
/imgs/63x128MiB+4KiB.img: ********** WARNING: Filesystem still has errors **********
/imgs/63x128MiB+4KiB.img: 11/524288 files (0.0% non-contiguous), 32737/2064385 blocks
----------------------------------------
Requested Size: 8GiB
Content: none
Size: FAIL
allocatedMiB <= ceilingMiB = false; allocatedMiB = 129; ceilingMiB = 32
e2fsck: FAIL rc=4
Block bitmap differences:  +(32768--32930)
Fix? no
/imgs/8GiB.img: ********** WARNING: Filesystem still has errors **********
/imgs/8GiB.img: 11/524288 files (0.0% non-contiguous), 32737/2097152 blocks
----------------------------------------
Requested Size: 16GiB
Content: none
Size: FAIL
allocatedMiB <= ceilingMiB = false; allocatedMiB = 258; ceilingMiB = 32
e2fsck: FAIL rc=4
Block bitmap differences:  +(32768--65826)
Fix? no
/imgs/16GiB.img: ********** WARNING: Filesystem still has errors **********
/imgs/16GiB.img: 11/1048576 files (0.0% non-contiguous), 32737/4194304 blocks
----------------------------------------
Requested Size: 160MiB
Content: 10MiB
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 128MiB
Content: 50MiB
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 160MiB
Content: 120MiB
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 160MiB
Content: 124MiB
Size: PASS
e2fsck: FAIL rc=4
Block bitmap differences:  +(32768--32806)
Fix? no
/imgs/160MiB_124MiB-content.img: ********** WARNING: Filesystem still has errors **********
/imgs/160MiB_124MiB-content.img: 135/16384 files (0.0% non-contiguous), 32737/40960 blocks
----------------------------------------
Requested Size: 160MiB
Content: 126MiB
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 256MiB
Content: 130MiB
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 1GiB
Content: 200MiB
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 300MiB
Content: 260MiB
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 4GiB
Content: 260MiB
Size: PASS
e2fsck: PASS
----------------------------------------
Requested Size: 63x128MiB
Content: 500MiB
Size: PASS
e2fsck: FAIL rc=4
Block bitmap differences:  +(131072--160417)
Fix? no
/imgs/63x128MiB_500MiB-content.img: ********** WARNING: Filesystem still has errors **********
/imgs/63x128MiB_500MiB-content.img: 511/516096 files (0.0% non-contiguous), 131041/2064384 blocks
----------------------------------------
Requested Size: 8GiB
Content: 300MiB
Size: PASS
e2fsck: FAIL rc=4
Block bitmap differences:  +(98304--109730)
Fix? no
/imgs/8GiB_300MiB-content.img: ********** WARNING: Filesystem still has errors **********
/imgs/8GiB_300MiB-content.img: 311/524288 files (0.0% non-contiguous), 98273/2097152 blocks
----------------------------------------
Requested Size: 16GiB
Content: 1000MiB
Size: PASS
e2fsck: FAIL rc=4
Block bitmap differences:  +(262144--321828)
Fix? no
/imgs/16GiB_1000MiB-content.img: ********** WARNING: Filesystem still has errors **********
/imgs/16GiB_1000MiB-content.img: 1011/1048576 files (0.0% non-contiguous), 262113/4194304 blocks
----------------------------------------