View.resizeEvent might be called with an empty size

[jimy-byerley]

it is possible that View.resizeEvent is called with a size with a null coordinate (especially when using layouts). When so, View.init fails to reinitialize framebuffers because is openGL doesn't allocate empty buffers
maybe it is better to ignore empty sizes ?

def resizeEvent(self, evt):
		QOpenGLWidget.resizeEvent(self, evt)
		self.handler.resize(self.size())
		if self.width() * self.height():
			self.init()
			self.update()