Fixed text drawing for vertex buffer output
Fixed text drawing for vertex buffer output

Previoulsy if you select text while using the vertex buffer
output inside a single line edit widget you would get a drawing bug
and the selected text would get transparent. This was caused by
overdraw by the selected text while the unselected text is still
visible.
To fix this behavior the text background is cleared before drawing.
This will cost another rectangle for each text which is quite
wasteful. Probably have to think about way to only draw the
rectangle if really necessary.

OpenMusicKontrollers/moony.lv2,OpenMusicKontrollers/synthpod,OpenMusicKontrollers/patchmatrix,OpenMusicKontrollers/midi_matrix.lv2,OpenMusicKontrollers/moony.lv2,OpenMusicKontrollers/patchmatrix,OpenMusicKontrollers/synthpod,OpenMusicKontrollers/sherlock.lv2,OpenMusicKontrollers/patchmatrix,OpenMusicKontrollers/patchmatrix,OpenMusicKontrollers/midi_matrix.lv2,OpenMusicKontrollers/moony.lv2,OpenMusicKontrollers/synthpod,glegris/nuklear4j,OpenMusicKontrollers/moony.lv2,OpenMusicKontrollers/moony.lv2,OpenMusicKontrollers/sherlock.lv2,OpenMusicKontrollers/synthpod,OpenMusicKontrollers/sherlock.lv2,glegris/nuklear4j,OpenMusicKontrollers/moony.lv2,OpenMusicKontrollers/sherlock.lv2,OpenMusicKontrollers/midi_matrix.lv2,OpenMusicKontrollers/synthpod,OpenMusicKontrollers/midi_matrix.lv2