Support subsetting in Android Generic Media provider

rime/providers/androidgenericmedia.py

@@ -55,7 +55,12 @@ def subset(self, subsetter, events, contacts):
         """
         Create a subset using the given events and contacts.
         """
-        return None
+        for event in events:
+            if event.provider.NAME != self.NAME:
+                continue
+
+            with self.fs.open(event.local_id) as h:
+                subsetter.copy_file(h, event.local_id)
 
     def all_files(self):
         # TODO
@@ -65,6 +70,9 @@ def search_events(self, device, filter_):
         """
         Search for events matching ``filter_``, which is an EventFilter.
         """
+        if not self.fs.exists('/sdcard'):
+            return []
+
         for direntry in self.fs.walk('/sdcard'):
             if not direntry.mime_type:
                 continue