Don't show dialogs from OnExceptionInMainLoop() in the tests

Similarly to the previous commit, ensure that the tests can run
unattended under MSW even if an unhandled exception is thrown during
their execution.

tests/test.cpp

@@ -219,6 +219,16 @@ public:
     }
 #endif // __WIN32__
 
+    // Also override this method to avoid showing any dialogs from here -- and
+    // show some details about the exception along the way.
+    virtual bool OnExceptionInMainLoop()
+    {
+        wxFprintf(stderr, "Unhandled exception in the main loop: %s\n",
+                  Catch::translateActiveException());
+
+        throw;
+    }
+
     // used by events propagation test
     virtual int FilterEvent(wxEvent& event);
     virtual bool ProcessEvent(wxEvent& event);