Fix menu bar background colour in wxQt

wxMenuBar is a native, not generic, window, so pass "false" to
PostCreation() to use the correct colours for it.

docs/changes.txt

@@ -107,6 +107,10 @@ wxOSX:
 
 - Fix dispatching pending events (and CallAfter()) in console applications.
 
+wxQt:
+
+- Fix menu bar background colour (Naser Buhamad).
+
 
 3.1.1: (released 2018-02-19)
 ----------------------------

src/qt/menu.cpp

@@ -162,13 +162,13 @@ QMenu *wxMenu::GetHandle() const
 wxMenuBar::wxMenuBar()
 {
     m_qtMenuBar  = new QMenuBar();
-    PostCreation();
+    PostCreation(false);
 }
 
 wxMenuBar::wxMenuBar( long WXUNUSED( style ))
 {
     m_qtMenuBar = new QMenuBar();
-    PostCreation();
+    PostCreation(false);
 }
 
 wxMenuBar::wxMenuBar(size_t count, wxMenu *menus[], const wxString titles[], long WXUNUSED( style ))
@@ -178,7 +178,7 @@ wxMenuBar::wxMenuBar(size_t count, wxMenu *menus[], const wxString titles[], lon
     for ( size_t i = 0; i < count; ++i )
         Append( menus[ i ], titles[ i ] );
 
-    PostCreation();
+    PostCreation(false);
 }