Don't attempt to cache glyph metrics for FONT_INVALID_CODE

This was causing massive slowdown in redisplay when eg #xfe0f
(VARIATION SELECTOR-16) was present, as the cache ended up very large,
unused, and being recreated on every call to font_fill_lglyph_metrics

* src/composite.c (fill_gstring_body): Hoist FONT_OBJECT_P check out
of loop.  Calculate glyph code and check for FONT_INVALID_CODE before
calling font_fill_lglyph_metrics.  Pass glyph code to it.

* src/font.c (font_fill_lglyph_metrics): Add code parameter, move
glyph code calculation up the call stack into fill_gstring_body.

* src/font.h: Adjust font_fill_lglyph_metrics prototype.
1 job for emacs-27 in 55 minutes and 44 seconds (queued for 2 seconds)
Status Job ID Name Coverage
failed #5128


Name Stage Failure
test-all Test
Makefile:319: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 2
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:294: 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