config parser: do not output garbage when braces are unbalanced

refs #172

src/knot/conf/cf-lex.l

@@ -303,8 +303,10 @@ hmac-sha512     { lval.alg = KNOT_TSIG_ALG_HMAC_SHA512; return TSIG_ALGO_NAME; }
 	char *name = conf_includes_pop(yyextra->includes);
 	free(name);
 	yypop_buffer_state(yyscanner);
-	if (!YY_CURRENT_BUFFER)
+
+	if (!YY_CURRENT_BUFFER) {
 		return END;
+	}
 }
 
 <include>{BLANK}+

src/knot/conf/conf.c

@@ -73,14 +73,17 @@ static void cf_print_error(void *scanner, const char *msg)
 	if (scanner) {
 		extra = cf_get_extra(scanner);
 		lineno = cf_get_lineno(scanner);
-		text = cf_get_text(scanner);
 		filename = conf_includes_top(extra->includes);
-
 		extra->error = true;
 	}
 
-	if (!filename)
+	if (extra && lineno != 0) {
+		text = cf_get_text(scanner);
+	}
+
+	if (!filename) {
 		filename = new_config->filename;
+	}
 
 	log_server_error("Config error in '%s' (line %d token '%s') - %s\n",
 			 filename, lineno, text, msg);

src/knot/conf/extra.c

@@ -29,8 +29,9 @@
 conf_extra_t *conf_extra_init(const char *file, int includes_max_depth)
 {
 	conf_extra_t *extra = calloc(1, sizeof(conf_extra_t));
-	if (!extra)
+	if (!extra) {
 		return NULL;
+	}
 
 	conf_includes_t *includes = conf_includes_init(includes_max_depth);
 	if (!includes) {