Check is allocation in event queue was success or not, and

report error / assert when allocation fails.

equeue.c

@@ -566,18 +566,22 @@ static void equeue_chain_update(void *p, int ms) {
     }
 }
 
-void equeue_chain(equeue_t *q, equeue_t *target) {
+int equeue_chain(equeue_t *q, equeue_t *target) {
     if (!target) {
         equeue_background(q, 0, 0);
-        return;
+        return 0;
     }
 
     struct equeue_chain_context *c = equeue_alloc(q,
             sizeof(struct equeue_chain_context));
+    if (!c) {
+        return -1;
+    }
 
     c->q = q;
     c->target = target;
     c->id = 0;
 
     equeue_background(q, equeue_chain_update, c);
+    return 0;
 }

equeue.h

@@ -206,7 +206,10 @@ void equeue_background(equeue_t *queue,
 //
 // The equeue_chain function allows multiple equeues to be composed, sharing
 // the context of a dispatch loop while still being managed independently.
-void equeue_chain(equeue_t *queue, equeue_t *target);
+//
+// If the event queue chaining fails, equeue_chain returns a negative,
+// platform-specific error code.
+int equeue_chain(equeue_t *queue, equeue_t *target);
 
 
 #ifdef __cplusplus