Fix advance of zero-width spaces in fonts that omits the glyph

Some fonts appear to include zero-width space in the CMAP table, but
not include an actual definitions of the glyph they point to. The
missing glyph causes a warning, but isn't handled making the character
end up being giving the same metrics as whatever character it came after.

This patch adds explicit handling of missing glyphs, and also caches
their missing state when caching is enabled.

Task-number: QTBUG-40912
Change-Id: I06fba9c01df59548e750e36babfdd5a6bafd6bd0
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>

0 files changed, 0 insertions, 0 deletions