CTFontCreatePathForGlyph() will return NULL for blank glyphs causing
CoreTextStyle::GetGlyphOutline() to return false which propagated as
error all the way to OutputDevice::GetTextOutlines() causing it to
needlessly enter into fallback code. Other implementations just return
true and an empty polygon here.

Change-Id: Ib20ebff00f7cb3aae22f1c6b4c3a0e9d7a429987
Reviewed-on: https://gerrit.libreoffice.org/31902Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Khaled Hosny <khaledhosny@eglug.org>