tracker-search-bar: Fixed results window show/hide semantics.
tracker-search-bar: Fixed results window show/hide semantics.

- Now the search results window is hidden if the text is NULL or "".
- Now the search results window is shown if a previous item is
  activated in the list and a new search term is typed

hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker