Fix log follow mode

When using a range with an explicit num_entries systemd-journal-gatewayd
will not contiue even when the follow parameter is passed.

Fixes an issue introduced with #5334.

supervisor/api/host.py

@@ -239,11 +239,11 @@ async def advanced_logs_handler(
                 # return 2 lines at minimum.
                 lines = max(2, lines)
             # entries=cursor[[:num_skip]:num_entries]
-            range_header = f"entries=:-{lines-1}:{lines}"
+            range_header = f"entries=:-{lines-1}:{"" if follow else lines}"
         elif RANGE in request.headers:
             range_header = request.headers.get(RANGE)
         else:
-            range_header = f"entries=:-{DEFAULT_LINES-1}:{DEFAULT_LINES}"
+            range_header = f"entries=:-{DEFAULT_LINES-1}:{"" if follow else DEFAULT_LINES}"
 
         async with self.sys_host.logs.journald_logs(
             params=params, range_header=range_header, accept=LogFormat.JOURNAL