Fixed non-existent wxCairoContext default ctor.

wxCairoContext class declared default ctor which wasn't implemented and even
couldn't be implemented because its base class didn't have any default ctor
neither.

Fix this by providing a ctor taking wxGraphicsRenderer* and implement it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69354 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/graphicc.cpp

@@ -354,7 +354,10 @@ public:
 #endif
     wxCairoContext( wxGraphicsRenderer* renderer, cairo_t *context );
     wxCairoContext( wxGraphicsRenderer* renderer, wxWindow *window);
-    wxCairoContext();
+
+    // If this ctor is used, Init() must be called by the derived class later.
+    wxCairoContext( wxGraphicsRenderer* renderer );
+
     virtual ~wxCairoContext();
 
     virtual bool ShouldOffset() const
@@ -1660,6 +1663,12 @@ wxCairoContext::wxCairoContext( wxGraphicsRenderer* renderer, wxWindow *window)
 
 }
 
+wxCairoContext::wxCairoContext(wxGraphicsRenderer* renderer) :
+    wxGraphicsContext(renderer)
+{
+    m_context = NULL;
+}
+
 wxCairoContext::~wxCairoContext()
 {
     if ( m_context )