LibGfx: Don't try to paint glyphs that aren't in a font

[awesomekling]

Fixes #88

[AtkinsSJ]

Should this try to draw the "missing character" symbol instead? Or is that already handled somewhere else.

[awesomekling]

Should this try to draw the "missing character" symbol instead? Or is that already handled somewhere else.

If we wanted to draw the "missing character", we should have figured that out much earlier and asked to draw the missing character glyph :)

[awesomekling]

If we didn't choose the missing character glyph earlier, we most likely think whatever we're drawing will fit into 0x0 space as well 😅

[AtkinsSJ]

Yeah I'm just a little confused how we end up here without a valid glyph. It's fine as a "just in case" check, it's just odd that we're hitting it.