rcfile: properly handle an empty syntax before an 'include' statement

So that in the error message the correct filename gets shown
instead of the name of the (first) include file.

Reported-by: Brand Huntsman <alpha@qzx.com>

src/rcfile.c

@@ -631,6 +631,8 @@ void parse_includes(char *ptr)
 	glob_t files;
 	int result;
 
+	check_for_nonempty_syntax();
+
 	pattern = ptr;
 	if (*pattern == '"')
 		pattern++;