Skip processing of blank lines in CSV input and ensure minimum column count

[drbergman]

For misspecified cells.csv rows, the error is a cryptic segfault. This makes the error clear and also skips over any blank lines, including a file that ends with two blank lines. Now, the following cells.csv files work for the template project (with initial condition enabled)

extra blank line at end:

x,y,z,type
0,0,0,default

skipped line (perhaps to separate cell types or just an innocent mistake):

x,y,z,type
0,0,0,default

10,0,0,default

throws a clear error message on misspecified csvs:

x,y,z,type
0,0,0,default
0,1,default

[Copilot]

Pull request overview

This PR improves robustness of CSV-based initial condition loading by skipping blank lines and adding early validation to avoid cryptic crashes when parsing malformed cells.csv rows.

Changes:

• Skip processing of empty/blank lines when loading v1 CSV cell position files.
• Add a minimum-column-count check for v2 CSV row parsing to fail fast with a clearer error.

Comments suppressed due to low confidence (1)

modules/PhysiCell_geometry.cpp:748

• process_csv_v2_line() only checks tokens.size()==0 for blank lines, but whitespace-only lines will produce a single token and currently hard-error. Also, later code indexes labels[k] up to tokens.size()-1; if a row has more columns than the header, this will read past labels and can still segfault on malformed CSVs. Consider treating whitespace-only lines as blank and validating tokens/labels column counts before continuing.

	// check that we have enough tokens and protect against blank lines
	if ( tokens.size() == 0 )
	{ return NULL; }
	else if (tokens.size() < 4)
	{

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