Fix M5.Power.powerOFF() exception bug (#225)

* Fix M5Power.powerOFF() exception bug, adapt related example to new Power-API.

* wifi check better using esp_wifi_get_mode()

Author: prjh

examples/Basics/PowerOFF/PowerOFF.ino

@@ -14,15 +14,16 @@ void setup(){
   M5.Power.begin();
 
   // Lcd display
-  M5.Lcd.println("This is software power off demo");
-  M5.Lcd.println("Press the button A to power off.");
+  M5.Lcd.setTextSize(2);
+  M5.Lcd.println("Software Power-OFF Demo");
+  M5.Lcd.println("Press Button A ...");
 }
 
 // the loop routine runs over and over again forever
 void loop() {
 
   if(M5.BtnA.wasPressed()) {
-    M5.powerOFF();
+    M5.Power.powerOFF();
   }
 
   M5.update();

src/utility/Power.cpp

@@ -392,9 +392,12 @@ void POWER::powerOFF(){
     M5.I2C.writeByte(IP5306_ADDR, IP5306_REG_SYS_CTL1, (data & (~BOOST_ENABLE_BIT)));
   }
 
-  //stop wifi
-  esp_wifi_disconnect();
-  esp_wifi_stop();
+  // if wifi was initialized, stop it
+  wifi_mode_t mode;
+  if (esp_wifi_get_mode(&mode) == ESP_OK) {
+    esp_wifi_disconnect();
+    esp_wifi_stop();
+  }
 
   //stop bt
   esp_bluedroid_disable();