PathFilter::setFilter: don't copy items before overwriting them
Average BenchQuickOpen::benchProjectFileFilter_setFilter
results before
and at this commit in milliseconds per iteration:
Data row Before At
1000- 0.0018 0.0018
1000-bar 0.55 0.50
1000- 1 0.57 0.49
1000-f/b 0.47 0.41
10000- 0.0018 0.0018
10000-bar 5.8 5.3
10000- 1 5.5 4.7
10000-f/b 5.0 4.4