Clear parsing_heredoc at the end of file

mrbgems/mruby-compiler/core/parse.y

@@ -3946,6 +3946,7 @@ parse_string(parser_state *p)
           }
         }
         if ((len-1 == hinf->term_len) && (strncmp(s, hinf->term, len-1) == 0)) {
+          if (c < 0) p->parsing_heredoc = NULL;
           return tHEREDOC_END;
         }
       }