Dismiss the Slice-Plate Popup Before the Filament Grouping Dialog Opens

The Slice-plate hover popup (FilamentGroupPopup, a wxPopupTransientWindow)
takes the mouse capture while it is shown, and on macOS its OnIdle handler
reacquires that capture whenever the cursor sits outside the popup. If the
popup is still shown when the modal filament grouping dialog opens, wx routes
every dialog mouse event to the now-hidden popup, because WX_filterSendEvent
short-circuits to the capture window while GetCapture() is non-null. The
dialog's filament blocks never receive a mouse-down, so they can't be dragged
and the whole app looks frozen even though its modal loop is healthy and the
keyboard still works.

Dismiss the popup synchronously before the dialog opens: Dismiss() hides it
and releases the capture, and hiding it stops OnIdle from reacquiring. This is
a no-op where the popup is never shown (Linux, where the hover popup is
disabled, and any non-dual-nozzle printer).

src/slic3r/GUI/FilamentGroupPopup.hpp

@@ -29,6 +29,7 @@ public:
     FilamentGroupPopup(wxWindow *parent);
     void tryPopup(Plater* plater,PartPlate* plate, bool slice_all);
     void tryClose();
+    void Dismiss() override;
 
     FilamentMapMode GetSelectedMode() const { return m_mode; }
 private:
@@ -40,7 +41,6 @@ private:
     void OnLeaveWindow(wxMouseEvent &);
     void OnEnterWindow(wxMouseEvent &);
     void OnTimer(wxTimerEvent &event);
-    void Dismiss();
 
     void CreateBmps();
 

src/slic3r/GUI/MainFrame.cpp

@@ -2309,6 +2309,12 @@ wxBoxSizer* MainFrame::create_side_tools()
 
             bool slice = true;
 
+            // The Slice-plate hover popup is a transient popup that keeps grabbing
+            // the mouse capture while shown. Left behind the modal grouping dialog it
+            // would starve that dialog of mouse events, so close it synchronously first.
+            if (m_filament_group_popup)
+                m_filament_group_popup->Dismiss();
+
             auto curr_plate = m_plater->get_partplate_list().get_curr_plate();
             #ifdef __linux__
                 PresetBundle* preset = wxGetApp().preset_bundle;