When we find an error in a yara file, exit instead of continuing to p…

…arse

The yara parser can potentially overwrite heap buffers parsing invalid yara files.
Exit on error to avoid this.  These overwrites are only observed when running
with address sanitization and mpool disabled.

libclamav/yara_grammar.c

@@ -3649,6 +3649,8 @@ YYSTYPE yylval YY_INITIAL_VALUE (= yyval_default);
       }
 # undef YYSYNTAX_ERROR
 #endif
+      /*Exit out, no reason to continue parsing, since we have already found errors.*/
+      goto yyreturn;
     }