Don't use invalid static_cast<> in wxAppConsoleBase ctor

Although the object being created _will_ be of type wxAppConsole, it
doesn't have this type yet, as wxAppConsole ctor hadn't yet run, and so
the static cast is invalid and detected as such by UBSAN in g++ 6.3.

src/common/appbase.cpp

@@ -173,7 +173,7 @@ wxAppConsoleBase::wxAppConsoleBase()
     m_mainLoop = NULL;
     m_bDoPendingEventProcessing = true;
 
-    ms_appInstance = static_cast<wxAppConsole *>(this);
+    ms_appInstance = reinterpret_cast<wxAppConsole *>(this);
 
 #ifdef __WXDEBUG__
     SetTraceMasks();