Fix to allow opening popup from a left-click on void or another window (because left-click would normally override focus immediately) (#126)

Neither appears to be really useful frankly.

imgui.cpp

@@ -2376,6 +2376,8 @@ void ImGui::Render()
 
         // Click to focus window and start moving (after we're done with all our widgets)
         if (g.ActiveId == 0 && g.HoveredId == 0 && g.IO.MouseClicked[0])
+        {
+            if (!(g.FocusedWindow && !g.FocusedWindow->WasActive && g.FocusedWindow->Active)) // Unless we just made a popup appear
             {
                 if (g.HoveredRootWindow != NULL)
                 {
@@ -2389,6 +2391,7 @@ void ImGui::Render()
                     FocusWindow(NULL);
                 }
             }
+        }
 
         // Sort the window list so that all child windows are after their parent
         // We cannot do that on FocusWindow() because childs may not exist yet