Adds null checks on callers of Nullable method getA11yServiceInfo().

Also renames mPackageName to mFeatureName. This string is used as the
user-visible feature name, e.g. TalkBack, not the APK package name.

Fix: 382054546
Test: n/a (existing presubmit)
Flag: EXEMPT minor bugfix
Change-Id: I1ce6902612d89bbb68bddf30227ca231ea98dce7

src/com/android/settings/accessibility/LaunchAccessibilityActivityPreferenceFragment.java

@@ -81,7 +81,7 @@ public class LaunchAccessibilityActivityPreferenceFragment extends ToggleFeature
         super.onProcessArguments(arguments);
         mComponentName = arguments.getParcelable(AccessibilitySettings.EXTRA_COMPONENT_NAME);
         final ActivityInfo info = getAccessibilityShortcutInfo().getActivityInfo();
-        mPackageName = info.loadLabel(getPackageManager()).toString();
+        mFeatureName = info.loadLabel(getPackageManager());
 
         // Settings animated image.
         final int animatedImageRes = arguments.getInt(