Examples: Viewport: Moved the "make current GL context" to reduce the amount of call and hopefully be more explicit about viewport enabled vs disabled requirements. (#1542)

examples/example_glfw_opengl2/main.cpp

@@ -140,9 +140,9 @@ int main(int, char**)
         {
             ImGui::UpdatePlatformWindows();
             ImGui::RenderPlatformWindowsDefault();
+            glfwMakeContextCurrent(window);
         }
 
-        glfwMakeContextCurrent(window);
         glfwSwapBuffers(window);
     }