Fix fieldml session not cleaning up global xml error messages causing successive reading not possible once a fieldml document error has been encountered.

Author: alan-wu

core/src/FieldmlDOM.cpp

@@ -156,6 +156,8 @@ static int validate( FieldmlErrorHandler *errorHandler, xmlParserInputBufferPtr
         errorHandler->logError( errorMessage );
     }
 
+    xmlResetLastError();
+
     return result;
 }