BUG: Add additional check

Source/cmCTest.cxx

@@ -179,6 +179,10 @@ std::string cmCTest::MakeXMLSafe(const std::string& str)
         }
       }
     }
+  if ( result.size() == 0 )
+    {
+    return "";
+    }
   return std::string(&*result.begin(), result.size());
 }