Address regression in [0] which allowed wmKeyMapItem::properties to
remain set when a valid wmKeyMapItem::ptr can't be created because the
wmOperatorType isn't available (temporarily in the case of reloading).
Resolve by freeing wmKeyMapItem::properties when the `ptr` isn't set.
Also add null pointer check not to assume wmKeyMapItem::properties
implies an allocated wmKeyMapItem::ptr. Something which is already
accounted for everywhere else.
[0]: 08e5f94a70
8ee209cb77