resolve RTWInterface initialization run after error issue

Author: Archcady

targets/TARGET_Realtek/TARGET_AMEBA/RTWInterface.cpp

@@ -93,12 +93,14 @@ RTWInterface::RTWInterface()
 
     emac = wlan_emac_init_interface();
     if (!emac) {
-       printf("Error init RTWInterface!\r\n");
+        printf("Error init RTWInterface!\r\n");
+        return;
     }
     emac->ops.power_up(emac);
     ret = mbed_lwip_init(emac);
     if (ret != 0) {
         printf("Error init RTWInterface!(%d)\r\n", ret);
+        return;
     }
 }
 

targets/TARGET_Realtek/TARGET_AMEBA/rtw_emac.cpp

@@ -218,6 +218,10 @@ emac_interface_t *wlan_emac_init_interface()
 
     if (_emac == NULL) {
         _emac = new emac_interface_t();
+    	if (_emac == NULL) {//new emac_interface_t fail
+        	printf("emac initialization failed\r\n");
+		return NULL;
+    	}
         _emac->hw = NULL;
         memcpy((void*)&_emac->ops, &wlan_emac_interface, sizeof(wlan_emac_interface));
     }