Ensure that strings returned by wxMBConv_cf are in NFC form.

Normalize all Unicode strings used internally even though the Darwin kernel
gives them to us in decomposed (NFD) form.

Closes #11730.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66033 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/core/strconv_cf.cpp

@@ -90,6 +90,14 @@ WXDLLIMPEXP_BASE wxMBConv* new_wxMBConv_cf(wxFontEncoding encoding)
         if ( theString == NULL )
             return wxCONV_FAILED;
 
+        // Ensure that the string is in canonical composed form (NFC): this is
+        // important because Darwin uses decomposed form (NFD) for e.g. file
+        // names but we want to use NFC internally.
+        wxCFRef<CFMutableStringRef>
+            cfMutableString(CFStringCreateMutableCopy(NULL, 0, theString));
+        CFStringNormalize(cfMutableString, kCFStringNormalizationFormC);
+        theString = cfMutableString;
+
         /* NOTE: The string content includes the NULL element if the source string did
          * That means we have to do nothing special because the destination will have
          * the NULL element iff the source did and the NULL element will be included