0005995: search with spaces only causes MySQL exception

This fix trims the `searchparam` parameter before checking conditions indicating empty searches.
For further information see https://bugs.oxid-esales.com/view.php?id=5995

Space-only values for the other search related parameters (`searchcnid`, `searchvendor`, `searchmanufacturer`) don't cause the same effect (MySQL exception).

The root cause for this bug lies in `oxSearch::_getWhere()` and may need further treatment. But because OXID eShop should handle space-only searchparam values like empty values and because of my assumption that the other call traces to this method don't involve user input I implemented the trim-call in the search controller and added an unit test for this case.
Good taht you provided test, but it is not ok because you used our legacy stuff with modConfig and addFunction we do not use it any more (but yes it is still left in older tests).