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/ToggleAccessibilityServicePreferenceFragment.java

@@ -385,8 +385,8 @@ public class ToggleAccessibilityServicePreferenceFragment extends
         }
 
         // Get Accessibility service name.
-        mPackageName = getAccessibilityServiceInfo().getResolveInfo().loadLabel(
-                getPackageManager());
+        AccessibilityServiceInfo info = getAccessibilityServiceInfo();
+        mFeatureName = info == null ? "" : info.getResolveInfo().loadLabel(getPackageManager());
 
         if (arguments.containsKey(AccessibilitySettings.EXTRA_TILE_SERVICE_COMPONENT_NAME)) {
             final String tileServiceComponentName = arguments.getString(