Added missing checks for wifi_link_out when allocating packets

Author: andreas.larsson

targets/TARGET_STM/TARGET_STM32F4/TARGET_UBLOX_EVK_ODIN_W2/sdk/wifi_emac/wifi_emac_api.cpp

@@ -267,9 +267,16 @@ static bool wifi_link_out(emac_interface_t *emac, emac_stack_mem_t *buf)
     (void)emac;
 	// Break call chain to avoid the driver affecting stack usage for the IP stack thread too much
     emac_stack_mem_t *new_buf = emac_stack_mem_alloc(emac, emac_stack_mem_chain_len(emac,buf),0);
-    emac_stack_mem_copy(emac,new_buf,buf);
-    cbMAIN_getEventQueue()->call(send_packet,emac,new_buf);
-    cbMAIN_dispatchEventQueue();
+    if (new_buf != NULL) {
+        emac_stack_mem_copy(emac, new_buf, buf);
+        int id = cbMAIN_getEventQueue()->call(send_packet, emac, new_buf);
+        if (id != 0) {
+            cbMAIN_dispatchEventQueue();        
+        }
+        else {
+            emac_stack_mem_free(emac, new_buf);
+        }
+    }
     return true;
 }