vao init upon bind fix

+ fixes an issue where a newly created vao might not be filled with values, since it would be kept unchanged. A newly created vao is marked as changed, i.e. dirty

to reproduce:

`ofNofill();
ofSetColor(ofColor::yellow);
ofDrawRectangle(ofRectangle(...)); // will not draw`
Merge pull request #3380 from tgfrerer/fix-vao-changed-upon-initialisation

vao init upon bind fix