gmain: simplify handling child watchers in dispatch_unix_signals_unlocked()

- if a child watch source has "using_pidfd", it is never linked in the
  unix_child_watches list. Drop that check.
- replace the deep nested if, with an early "continue" in the loop,
  if we detect there is nothing to do. It makes the code easier to
  read.

glib/gmain.c

@@ -5695,11 +5695,11 @@ dispatch_unix_signals_unlocked (void)
       for (node = unix_child_watches; node; node = node->next)
         {
           GChildWatchSource *source = node->data;
-
-          if (!source->using_pidfd &&
-              !g_atomic_int_get (&source->child_exited))
-            {
           pid_t pid;
+
+          if (g_atomic_int_get (&source->child_exited))
+             continue;
+
           do
             {
               g_assert (source->pid > 0);
@@ -5721,7 +5721,6 @@ dispatch_unix_signals_unlocked (void)
           while (pid == -1 && errno == EINTR);
         }
     }
-    }
 
   /* handle GUnixSignalWatchSource instances */
   for (node = unix_signal_watches; node; node = node->next)