This reverts commit 06d24a79.

The CVE is still fixed but now in a different way. Commit 4fa0cd4d
passes instead the accurate string length when using the string, hence
making it work even when not NUL-terminated. This has the advantage of
having the GBR file loaded in the end, despite such file format error. I
am personally not persuaded this is the best path since a file with such
an error may either be corrupted, or worse may have been constructed on
purpose to be harmful, so rejecting it directly may be the safe choice.
Nevertheless I may also be too doubtful and maybe trying to save a
slightly corrupted file may be the nicest choice indeed.