gspawn-win32: Fix potential integer overflows in argv handling

Philip Withnallrequested to merge
pwithnall/glib:protect-argv-string into main

This can happen if a user passes a ludicrously long string to argv.

Spotted by chamalsl as #YWH-PGM9867-48.

Signed-off-by: Philip Withnall pwithnall@gnome.org

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