Fix tree.c->dirbrowse panic from database browser

I set up panics on invalid entries throughout tree.c
dirbrowser was checking for file attributes even when the result
was unused, the database browser called this code with an
invalid (to the tagcache) index

This patch fixes that oversight and also adds __func__ to the
panics for easier sleuthing in the future

Change-Id: Ie1d6511423bba48125e4916b1c3049c048abaee0
1 file changed