authentication: Added missing variable assignment.

The `mAuthTokenType` variable is declared and assigned a null value but no value is subsequently assigned, making the null check later on redundant. The `AccountAuthenticator.KEY_AUTH_TOKEN_TYPE` extra value should therefore be assigned the `mAuthTokenType` value I'm assuming.

Signed-off-by: ardevd <edvard.holst@gmail.com>

src/main/java/com/owncloud/android/authentication/AuthenticatorActivity.java

@@ -585,7 +585,7 @@ public class AuthenticatorActivity extends AccountAuthenticatorActivity
         mAuthTokenType = null;
 
         if (extras != null) {
-            extras.getString(AccountAuthenticator.KEY_AUTH_TOKEN_TYPE);
+            mAuthTokenType = extras.getString(AccountAuthenticator.KEY_AUTH_TOKEN_TYPE);
         }
 
         if (mAuthTokenType == null) {