Add null check for mChannel object in WifiP2Settings

When user switch between settings of hotspot(Enable hotspot),
Internet(Enable Wifi) and Wifi-Direct(establish, disconnect and
forgot P2P connection).

mChannel becomes null during WiFi P2P user scenarios resulting
in Settings(com.android.settings) crash on enable Wifi.

This commit fixes mChannel IllegalArgumentException: Channel
needs to be initialized.

Test: manual test
Bug: 218608961
Change-Id: I72c67bcd1086afe2aa8d2c5521107e2d38e5b0bb

src/com/android/settings/wifi/p2p/WifiP2pSettings.java

@@ -353,6 +353,7 @@ public class WifiP2pSettings extends DashboardFragment
             mWifiP2pManager.requestDeviceInfo(mChannel, WifiP2pSettings.this);
             mIsIgnoreInitConnectionInfoCallback = false;
             mWifiP2pManager.requestNetworkInfo(mChannel, networkInfo -> {
+                if (mChannel == null) return;
                 mWifiP2pManager.requestConnectionInfo(mChannel, wifip2pinfo -> {
                     if (!mIsIgnoreInitConnectionInfoCallback) {
                         if (networkInfo.isConnected()) {