Do not finish activity when the input account doesn't exist

This is to avoid the caller getting the existing account list because
the prompt respond reveals that the input account does not exist.

Bug: 249981091
Test: robotest
Change-Id: I4bb8ecead8233780443b1cd1a8780983b7e4d5de

tests/robotests/src/com/android/settings/accounts/ChooseAccountPreferenceControllerTest.java

@@ -173,7 +173,7 @@ public class ChooseAccountPreferenceControllerTest {
                 mActivity);
         mController.displayPreference(mPreferenceScreen);
 
-        assertThat(mActivity.isFinishing()).isTrue();
+        assertThat(mActivity.isFinishing()).isFalse();
         assertThat(mPreferenceScreen.getPreferenceCount()).isEqualTo(0);
     }