[Fix] Fix utf8 validation for symbols options and empty strings

src/libmime/scan_result.c

@@ -529,7 +529,7 @@ rspamd_task_add_result_option (struct rspamd_task *task,
 
 		vlen = strlen (val);
 
-		if (!rspamd_fast_utf8_validate (val, vlen)) {
+		if (rspamd_fast_utf8_validate (val, vlen) == 0) {
 			opt_cpy = rspamd_str_make_utf_valid (val, vlen, &vlen,
 					task->task_pool);
 			val = opt_cpy;

src/libutil/str_util.c

@@ -3067,7 +3067,11 @@ rspamd_str_make_utf_valid (const guchar *src, gsize slen,
 	}
 
 	if (slen == 0) {
-		return NULL;
+		if (dstlen) {
+			*dstlen = 0;
+		}
+
+		return pool ? rspamd_mempool_strdup (pool, "") : g_strdup ("");
 	}
 
 	p = src;