commands.c: Better fix for the /search-without-query bug
commands.c: Better fix for the /search-without-query bug

search.c:search_add() already does the same check. The actual problem
wasn't that uit_search_create() and related functions didn't handle
empty search requests, the problem was that they take ownership of the
search query, regardless of whether they succeeded or not.
commands.c:c_search() didn't correctly handle this and wanted to free
the already-freed query on error, thus resulting in the crash.

Both fixes effectively have the same result, but this one is nicer.

Tilka/ncdc,Tilka/ncdc