Dismiss PackageInstallerActivity when SimpleErrorDialog cancelled

Otherwise the translucent Activity sticks around until another back
press.

Bug: 187221431

Test: manual, adb shell am start \
    -a android.intent.action.INSTALL_PACKAGE \
    -d "file:///the-apk-that-wasnt.apk" \
    -n com.google.android.packageinstaller/com.android.packageinstaller.PackageInstallerActivity

Change-Id: I80ecf62247c62d76a832676ed52c68f9aefcb54e

packages/PackageInstaller/src/com/android/packageinstaller/PackageInstallerActivity.java

@@ -23,6 +23,7 @@ import static android.view.WindowManager.LayoutParams.SYSTEM_FLAG_HIDE_NON_SYSTE
 import android.Manifest;
 import android.annotation.NonNull;
 import android.annotation.StringRes;
+import android.app.Activity;
 import android.app.AlertDialog;
 import android.app.AppGlobals;
 import android.app.AppOpsManager;
@@ -632,6 +633,12 @@ public class PackageInstallerActivity extends AlertActivity {
                     .setPositiveButton(R.string.ok, (dialog, which) -> getActivity().finish())
                     .create();
         }
+
+        @Override
+        public void onCancel(DialogInterface dialog) {
+            getActivity().setResult(Activity.RESULT_CANCELED);
+            getActivity().finish();
+        }
     }
 
     /**