unix-socket: address scan-build warning

  CC       unix-manager.o
unix-manager.c:258:13: warning: Use of memory after it is freed [unix.Malloc]
  258 |         if (item->fd == fd) {
      |             ^~~~~~~~
1 warning generated.

(cherry picked from commit 39dfcaf)

Author: victorjulien

src/unix-manager.c

@@ -252,9 +252,10 @@ static void UnixClientFree(UnixClient *c)
 static void UnixCommandClose(UnixCommand  *this, int fd)
 {
     UnixClient *item;
+    UnixClient *safe = NULL;
     int found = 0;
 
-    TAILQ_FOREACH(item, &this->clients, next) {
+    TAILQ_FOREACH_SAFE (item, &this->clients, next, safe) {
         if (item->fd == fd) {
             found = 1;
             break;