Fix a NPE in PackageInstaller

We were returing a null PermissionGroup object to a place
where this was not expected by design. The reason for that
was an incorrect fix for b/28241097. This CL reverts the
introduced regression and adds a null check just in case.

bug:27102458

Change-Id: I78f8107d0adf6bb2da5d8e11c5f3cf3c00fe36a2

src/com/android/packageinstaller/permission/model/AppPermissionGroup.java

@@ -162,10 +162,6 @@ public final class AppPermissionGroup implements Comparable<AppPermissionGroup>
             group.addPermission(permission);
         }
 
-        if (group.getPermissions().isEmpty()) {
-            return null;
-        }
-
         return group;
     }
 

src/com/android/packageinstaller/permission/model/PermissionApps.java

@@ -190,6 +190,10 @@ public class PermissionApps {
                     AppPermissionGroup group = AppPermissionGroup.create(mContext,
                             app, groupInfo, groupPermInfos, user);
 
+                    if (group == null) {
+                        continue;
+                    }
+
                     String label = mSkipUi ? app.packageName
                             : app.applicationInfo.loadLabel(mPm).toString();
                     PermissionApp permApp = new PermissionApp(app.packageName,