Protect against no space name
Protect against no space name

Without this the x-doc and wiki serializations will raise a 404
when visiting a tiddlers collection from the main server_host (e.g.
tiddlyspace.com instead of cdent.tiddlyspace.com) because space_name
is not set whehn calling determine_space_recipe.

Fixes #1080

TiddlySpace/tiddlyspace,TiddlySpace/tiddlyspace,TiddlySpace/tiddlyspace