do not use invalid Directory instance (OSL_ASSERT about a NULL pointer)

Change-Id: Icc1dffc9b63453575ab927a3bdfa4b25cecfe8f2

vcl/source/gdi/temporaryfonts.cxx

@@ -20,7 +20,8 @@ void TemporaryFonts::clear()
     rtl::Bootstrap::expandMacros( path );
     path += "/user/temp/fonts/";
     osl::Directory dir( path );
-    dir.reset();
+    if( dir.reset() == osl::Directory::E_None )
+    {
         for(;;)
         {
             osl::DirectoryItem item;
@@ -31,6 +32,7 @@ void TemporaryFonts::clear()
                 osl::File::remove( status.getFileURL());
         }
     }
+}
 
 OUString TemporaryFonts::fileUrlForFont( const OUString& fontName, const char* fontStyle )
 {