Recreate macOS color list if it is corrupt

* src/nsterm.m (ns_term_init): Generate the color list if there are
less colors in the existing file than in rgb.txt.
1 job for master in 69 minutes and 36 seconds (queued for 1 second)
Status Job ID Name Coverage
failed #6789


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