Line height will adapt to font selected for invisible characters

If a font is selected for a character, the line height will be adjusted to accommodate for this font, even if the character is not visible. This can cause unexpected issues when some font on the system contains a glyph for a control character, since we currently do look these up in the fonts.

One solution for it would be to be smarter in the font selection algorithm and ignore control chars here. This would also increase performance in some cases.