[QueryTest] Add test case for terms folded to empty strings
The termgenerator removes leading, trailing and isolated punctuation characters. While this is no problem for leading or trailing punctuation as the normalized term is still non-empty, isolated punctuation ends up as an empty string.
The matcher then tries to find e.g. "(content:'' OR filename:'')", which returns not results, instead of the exptedted "everything". Unfortunately it is non-trivial to remove such Terms.
For the prase test, this is not at problem, as it always sees the whole phrase and can just skip the problematic part.