Fix (unreported) wrong handling of usercount in BKE_workspace_add().

This does not seem to be an actual issue in current master code (as
creating a new ID will assign 1 user to it by default), but is breaking
generic usercount handling in future changes.

source/blender/blenkernel/intern/workspace.c

@@ -146,6 +146,7 @@ static bool UNUSED_FUNCTION(workspaces_is_screen_used)
 WorkSpace *BKE_workspace_add(Main *bmain, const char *name)
 {
   WorkSpace *new_workspace = BKE_libblock_alloc(bmain, ID_WS, name, 0);
+  id_us_ensure_real(&new_workspace->id);
   return new_workspace;
 }