fix(android): Check if NetworkInfo is null to avoid crashes (#66)

Previously the `networkInfo` could be `null` and it would cause a crash when we try to decide the network type. This adds a `null` check to avoid this.

android/src/main/java/com/reactnativecommunity/netinfo/ConnectivityReceiver.java

@@ -91,6 +91,10 @@ public void setNoNetworkPermission() {
   }
 
   String getEffectiveConnectionType(NetworkInfo networkInfo) {
+    if (networkInfo == null) {
+      return EFFECTIVE_CONNECTION_TYPE_UNKNOWN;
+    }
+
     switch (networkInfo.getSubtype()) {
       case TelephonyManager.NETWORK_TYPE_1xRTT:
       case TelephonyManager.NETWORK_TYPE_CDMA: