HomeTrait does not load map (LOAD_MULTI_MAP) when map_present == 0 on single-map devices #985

Problem

When a vacuum has a saved and selected map (current_map is valid in GET_STATUS, and GET_MULTI_MAPS_LIST returns the map), the device can still report map_present: 0 in GET_STATUS while idle/docked (meaning the map is not currently loaded in the vacuum's active memory).

When GET_MAP_V1 is called while map_present == 0:

• The device returns an empty image block (width=0, height=0).
• vacuum-map-parser-roborock / vacuum-map-parser-base renders the "NO MAP" placeholder image (map_data.image.is_empty == True).

Currently in roborock/devices/traits/v1/home.py:

1. HomeTrait._build_home_map_info() only calls await self._maps_trait.set_current_map(map_info.map_flag) (RoborockCommand.LOAD_MULTI_MAP) when len(sorted_map_infos) > 1:

   for map_info in sorted_map_infos:
       # We need to load each map to get its room data
       if len(sorted_map_infos) > 1:
           ...
           await self._maps_trait.set_current_map(map_info.map_flag)

   When a user only has a single saved map (multi_map_count: 1), set_current_map is skipped even when self._status_trait.map_present == 0, and the resulting "NO MAP" response is persisted into DeviceCache.
2. HomeTrait.refresh() also does not check self._status_trait.map_present == 0 to reload the current map via set_current_map() before fetching GET_MAP_V1.

Expected Behavior

• During HomeTrait.discover_home() / _build_home_map_info() and HomeTrait.refresh(), if self._status_trait.map_present == 0 (and the device is not busy/cleaning/returning), HomeTrait should load the map via self._maps_trait.set_current_map(...) (handling RoborockInvalidStatus -> RoborockDeviceBusy and sleeping MAP_SLEEP) before refreshing map content.
• Avoid caching empty placeholder maps (map_data.image.is_empty) in DeviceCache as valid discovered home map content.

References

• Original report: Roborock map shows "NO MAP" until already-selected map is manually reselected home-assistant/core#185133
• Related Home Assistant PR: Recover selected Roborock map when the device reports no map home-assistant/core#186678