SearchableText "foo **" with a standalone wildcard causes error

Fix the problem and make "foo **" result in the same query as "foo". This currently causes an 500 Internal Server Error.

One might argue that "foo **"  is not a valid query, to start with. However it can be expected as an input, thus it should not cause a cryptic error anyway. The fix should cause to yield the expected results by stripping out the standalone wildcard.