OpenGL: compatibility shader fix in pickingutils.glsl
OpenGL: compatibility shader fix in pickingutils.glsl

* fixes "implicit conversion from int to uint" on OpenGL 3.3


Sparkier/inviwo,inviwo/inviwo,inviwo/inviwo,inviwo/inviwo,inviwo/inviwo,Sparkier/inviwo,inviwo/inviwo,inviwo/inviwo,Sparkier/inviwo,Sparkier/inviwo,Sparkier/inviwo