fix an issue spotted by the Clang analyzer (leak in yacc/reader.c)

yacc/reader.c:1328:7: warning: Potential leak of memory pointed to by 'a_line'
      fprintf(f, ")\n# 0\n              ");
      ^~~~~~~

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@16333 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

yacc/reader.c

@@ -1336,6 +1336,7 @@ loop:
         fprintf(f, " : '%s))\n", plhs[nrules]->name);
       if (sflag)
         fprintf(f, "\n");
+      FREE(a_line);
       return;
     }
     putc(c, f);