Override wxApp::OnAssertFailure in L7Test.

We do nothing in this override.

wxASSERT_MSG would fail in LGridJsonCellRenderer::ProcessJsonValue and
in XmlHelper::ValidateXmlValue called by
LGridXmlCellRenderer::ProcessXmlValue. This happens with postgresql
only, when the corresponding database value is empty. The cell value
is set to [Invalid], and next rendering leads to a crash in debug build
only.
Why does wxASSERT_MSG fail? Why with postgresql and not with sqlite?

L7Test/L7Test.cpp

@@ -41,6 +41,10 @@ int L7Test::OnExit()
     return wxApp::OnExit();
 }
 
+void L7Test::OnAssertFailure(const wxChar* file, int line, const wxChar* func, const wxChar* cond, const wxChar* msg)
+{
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 L7Frame::L7Frame(wxWindow* parent, wxWindowID id, const wxString& title)