parser: Optimize 0-length string parsing
parser: Optimize 0-length string parsing

We were still creating the ICU parser and trying to feed it with
data, which turned out surprisingly expensive on deletes, as
"deleting" on FTS just replaces the text with "nothing", so we're
creating a parser for each of these.

This reduces the timing of the sparql delete in the previous commit
further down to:
real	1m7.029s
user	0m0.023s
sys	0m0.009s

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