Fixed depth test when rendering the picking texture

xs/src/slic3r/GUI/GLCanvas3D.cpp

@@ -3446,6 +3446,7 @@ void GLCanvas3D::_picking_pass() const
             ::glDisable(GL_MULTISAMPLE);
 
         ::glDisable(GL_BLEND);
+        ::glEnable(GL_DEPTH_TEST);
 
         ::glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);