standardizes processing of _delaying in lwIP callbacks (remove assert) (#6460)

Author: d-a-v

libraries/ESP8266WiFi/src/include/ClientContext.h

@@ -609,9 +609,10 @@ class ClientContext
         (void) err;
         (void) pcb;
         assert(pcb == _pcb);
-        assert(_delaying);
-        _delaying = false;
-        esp_schedule(); // break current delay()
+        if (_delaying) {
+            _delaying = false;
+            esp_schedule(); // break current delay()
+        }
         return ERR_OK;
     }