nearby: make sure places is initialized

On taking a look at the following stack trace:

  java.lang.NullPointerException: Attempt to invoke interface method 'java.util.Iterator java.util.List.iterator()' on a null object reference
  at fr.free.nrw.commons.nearby.fragments.NearbyParentFragment.updatePlaceList(NearbyParentFragment.java:777)
  at fr.free.nrw.commons.nearby.fragments.NearbyParentFragment.lambda$initFilterChips$10$NearbyParentFragment(NearbyParentFragment.java:730)
  at fr.free.nrw.commons.nearby.fragments.-$$Lambda$NearbyParentFragment$AGol6SoJlvIYd45Vbz6tTjDiWU4.onCheckedChanged(Unknown Source:2)
  at android.widget.CompoundButton.setChecked(CompoundButton.java:235)
  at com.google.android.material.chip.Chip.setChecked(Chip.java:665)
  at android.widget.CompoundButton.toggle(CompoundButton.java:150)
  ...

... it seems clear the 'places' list is trying to be iterated
in the updatePlaceList method when it is empty. This is resulting
in an NPE and consequently an app crash.

Avoid the same by ensuring it is always initialized to an empty list.

app/src/main/java/fr/free/nrw/commons/nearby/fragments/NearbyParentFragment.java

@@ -259,7 +259,7 @@ public class NearbyParentFragment extends CommonsDaggerSupportFragment
     /**
      * Saves response of list of places for the first time
      */
-    private List<Place> places;
+    private List<Place> places = new ArrayList<>();
 
     @NonNull
     public static NearbyParentFragment newInstance() {