Bug #21072 Duplicate key error in NDB references wrong key: use MAX_KEY to...

Bug #21072  Duplicate key error in NDB references wrong key: use MAX_KEY to signal unknown key: Added string initialization

sql/handler.cc

@@ -1107,6 +1107,7 @@ void handler::print_error(int error, myf errflag)
       {
 	/* Key is unknown */
 	str.length(0);
+	str.append("");
 	key_nr= -1;
       }
       else