Disable client state in OpenGL example after rendering.

Using the example code in another application that has other rendering
code can cause rendering bugs or memory access errors if client state
is not disabled.

examples/opengl_example/main.cpp

@@ -61,6 +61,9 @@ static void ImImpl_RenderDrawLists(ImDrawList** const cmd_lists, int cmd_lists_c
         }
     }
     glDisable(GL_SCISSOR_TEST);
+    glDisableClientState(GL_COLOR_ARRAY);
+    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
+    glDisableClientState(GL_VERTEX_ARRAY);
 }
 
 static const char* ImImpl_GetClipboardTextFn()