disable MSAA for the picking

MSAA can and will result in mixed colors which is a problem if we use
the color for the selection.

Change-Id: Ifbd6d37902069b26e714d2e3e5576fb767f9fbbf

chart2/source/view/main/GL3DRenderer.cxx

@@ -1651,10 +1651,12 @@ void OpenGL3DRenderer::SetPickingMode(bool bPickingMode)
     if(mbPickingMode)
     {
         glBindFramebuffer(GL_FRAMEBUFFER, mnPickingFbo);
+        glDisable(GL_MULTISAMPLE);
     }
     else
     {
         glBindFramebuffer(GL_FRAMEBUFFER, 0);
+        glEnable(GL_MULTISAMPLE);
     }
 }