fix creating dud progress entries

When the import process finishes it can set progress to 100 multiple
times.  The first call would add a stop time to the running progress,
but each further call with progress=100 would create another entry in
the table with stop already set.

unwind/db.py

@@ -136,6 +136,12 @@ async def set_import_progress(progress: float) -> Progress:
     progress = min(max(0.0, progress), 100.0)  # clamp to 0 <= progress <= 100
 
     current = await get_import_progress()
+    is_stopped = current and current.stopped is not None
+
+    if progress == 100.0 and is_stopped:
+        assert current
+        return current
+
     is_update = current and current.stopped is None
 
     if not current or not is_update: