Restore generic GetPartialTextExtents() version use in wxGTK and wxMSW.

Non-wxWindowDC-derived wxDC classes in wxGTK, such as wxGtkPrinterDCImpl, have
to fall back on the generic implementation of GetPartialTextExtents() as Pango
version can't be used with them.

This fixes a crash due to using NULL Pango layout when printing wxRichTextCtrl
in wxGTK.

Closes #14847.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73017 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/textmeasure.cpp

@@ -150,8 +150,11 @@ void wxTextMeasure::DoGetTextExtent(const wxString& string,
 
 bool wxTextMeasure::DoGetPartialTextExtents(const wxString& text,
                                             wxArrayInt& widths,
-                                            double WXUNUSED(scaleX))
+                                            double scaleX)
 {
+    if ( !m_hdc )
+        return wxTextMeasureBase::DoGetPartialTextExtents(text, widths, scaleX);
+
     static int maxLenText = -1;
     static int maxWidth = -1;