fix: Fix UB-sanitizer warning about alignment (#5097)

Signed-off-by: Larry Gritz <lg@larrygritz.com>

Author: lgritz

src/libOpenImageIO/exif.cpp

@@ -826,10 +826,11 @@ read_exif_tag(ImageSpec& spec, const TIFFDirEntry* dirp, cspan<uint8_t> buf,
     const TagMap& exif_tagmap(exif_tagmap_ref());
     const TagMap& gps_tagmap(gps_tagmap_ref());
 
-    // Make a copy of the pointed-to TIFF directory, swab the components
-    // if necessary.
+    // Make a copy of the pointed-to TIFF directory, swab the components if
+    // necessary. We have to do this as a memcpy rather than an assignment
+    // because the pointer we're copying from may not be properly aligned.
     TIFFDirEntry dir;
-    memcpy(&dir, dirp, sizeof(TIFFDirEntry));
+    memcpy(&dir, (const void*)dirp, sizeof(TIFFDirEntry));
     unsigned int unswapped_tdir_offset = dir.tdir_offset;
     if (swab) {
         swap_endian(&dir.tdir_tag);