Docking: Modals don't need to set ImGuiViewportFlags_NoFocusOnClick. …

…This also mitigate the common described by #2445, which becomes particularly bad with unfocused modal. (#1542)

imgui.cpp

@@ -6131,7 +6131,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
             // won't steal the OS focus away from their parent window (which may be reflected in OS the title bar decoration).
             // Setting _NoFocusOnClick would technically prevent us from bringing back to front in case they are being covered by an OS window from a different app, 
             // but it shouldn't be much of a problem considering those are already popups that are closed when clicking elsewhere.
-            if (is_short_lived_floating_window)
+            if (is_short_lived_floating_window && (flags & ImGuiWindowFlags_Modal) == 0)
                 viewport_flags |= ImGuiViewportFlags_NoFocusOnAppearing | ImGuiViewportFlags_NoFocusOnClick;
 
             // We can overwrite viewport flags using ImGuiWindowClass (advanced users)