alpm_list_remove treat NULL needle as "nothing"

So if you want to remove NULL needle from a list, alpm_list_remove will
return with "not found".

Signed-off-by: Nagy Gabor <ngaba@bibl.u-szeged.hu>
Signed-off-by: Dan McGee <dan@archlinux.org>

lib/libalpm/alpm_list.c

@@ -302,6 +302,10 @@ alpm_list_t SYMEXPORT *alpm_list_remove(alpm_list_t *haystack, const void *needl
 		*data = NULL;
 	}
 
+	if(needle == NULL) {
+		return(haystack);
+	}
+
 	while(i) {
 		if(i->data == NULL) {
 			continue;