ofMesh/ofVboMesh: draw returns if there's no vertices
ofGraphics: ofBackgroundGradient: use ofVboMesh
ofAppGLFWWindow: fix uninitialized variables
Merge branch 'feature-elinuxProgrammableGL' of git://github.com/arturoc/openFrameworks into feature-elinuxProgrammableGL

manually resolved

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>