nextcloud: Don't show incorrect phone region when it is not set

Tests:

- Install nextcloud and notice that the default phone region is 'Not set'.
Select phone region, it sets properly. Set it to 'Not set' and that works too.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/nextcloud/forms.py

@@ -11,9 +11,12 @@ def _get_phone_regions():
         from iso3166 import countries  # type: ignore
         phone_regions = [(country.alpha2, country.name)
                          for country in countries]
-        return sorted(phone_regions)
+        phone_regions = sorted(phone_regions)
     except ImportError:
-        return [('US', 'United States of America')]
+        # Allow users to set a non-empty value
+        phone_regions = [('US', 'United States of America')]
+
+    return [('', _('Not set'))] + phone_regions
 
 
 class NextcloudForm(forms.Form):

plinth/modules/nextcloud/views.py

@@ -25,7 +25,7 @@ class NextcloudAppView(AppView):
         initial = super().get_initial()
         initial.update({
             'domain': privileged.get_domain(),
-            'default_phone_region': privileged.get_default_phone_region()
+            'default_phone_region': privileged.get_default_phone_region() or ''
         })
         return initial