fix for potential crash when conversion fails

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@39886 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/mac/carbon/dc.cpp

@@ -1782,6 +1782,13 @@ bool wxDC::DoGetPartialTextExtents(const wxString& text, wxArrayInt& widths) con
 #endif
     {
         wxCharBuffer buff = text.mb_str(wxConvLocal);
+        if ( buff.data() == 0 )
+        {
+            for (size_t i=0; i<text.length(); i++)
+                widths[i] = 0 ;
+        }
+        else
+        {
             size_t len = strlen(buff);
             short* measurements = new short[len+1];
             MeasureText(len, buff.data(), measurements);
@@ -1794,6 +1801,7 @@ bool wxDC::DoGetPartialTextExtents(const wxString& text, wxArrayInt& widths) con
 
             delete [] measurements;
         }
+    }
 
     return true;
 }