Minor fix to recent coding.c change

* src/coding.c (get_buffer_gap_address):
Don’t assume string or buffer length fits in int.
Also, improve wording of comments.
1 job for master in 55 minutes and 40 seconds (queued for 3 seconds)
Status Job ID Name Coverage
failed #2890


Name Stage Failure
test-all Test
make[2]: *** [check-doit] Error 1
Makefile:318: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
make[1]: *** [check-expensive] Error 2
make: *** [check-expensive] Error 2
Makefile:293: recipe for target 'check-expensive' failed
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:959: recipe for target 'check-expensive' failed
ERROR: Job failed: exit code 1