Remove special wxFindReplaceDialog hack from wxGUIEventLoop

Don't call IsDialogMessage() for any unknown windows, this is not needed
any longer now that we recognize wxFindReplaceDialog HWND as ours (see
the previous commit) and that its MSWProcessMessage() works correctly
(done in this one).

Removing this IsDialogMessage() call still allows TAB navigation to work
in the "Find" dialog but prevents us from processing unknown messages
for unknown windows, which might have unwatned consequences.

include/wx/msw/fdrepdlg.h

@@ -41,6 +41,8 @@ public:
     virtual void SetTitle( const wxString& title) override;
     virtual wxString GetTitle() const override;
 
+    virtual bool MSWProcessMessage(WXMSG* pMsg) override;
+
 protected:
     virtual void DoGetSize(int *width, int *height) const override;
     virtual void DoGetClientSize(int *width, int *height) const override;

src/msw/evtloop.cpp

@@ -79,15 +79,7 @@ bool wxGUIEventLoop::PreProcessMessage(WXMSG *msg)
         }
 
         if ( !wndThis )
-        {
-            // this may happen if the event occurred in a standard modeless dialog (the
-            // only example of which I know of is the find/replace dialog) - then call
-            // IsDialogMessage() to make TAB navigation in it work
-
-            // NOTE: IsDialogMessage() just eats all the messages (i.e. returns true for
-            // them) if we call it for the control itself
-            return hwnd && ::IsDialogMessage(hwnd, msg) != 0;
-        }
+            return false;
     }
 
     if ( !AllowProcessing(wndThis) )

src/msw/fdrepdlg.cpp

@@ -446,6 +446,19 @@ wxString wxFindReplaceDialog::GetTitle() const
     return m_title;
 }
 
+// ----------------------------------------------------------------------------
+// wxFindReplaceDialog message handling
+// ----------------------------------------------------------------------------
+
+bool wxFindReplaceDialog::MSWProcessMessage(WXMSG* pMsg)
+{
+    // The base class MSWProcessMessage() doesn't work for us because we don't
+    // have wxTAB_TRAVERSAL style, but then we don't need it anyhow: as this
+    // dialog only ever contains standard controls, just using the standard
+    // function is enough to make TAB navigation work in it.
+    return m_hWnd && ::IsDialogMessage(m_hWnd, pMsg);
+}
+
 // ----------------------------------------------------------------------------
 // wxFindReplaceDialog position/size
 // ----------------------------------------------------------------------------