libflib: Add f_list_isempty/f_ptrlist_isempty.
libflib: Style fix.
libpacman: Use f_ptrlist_isempty in _pacman_db_get_pkgcache.
libpacman: Do not protect _pacman_db_search against NULL item in the ptrlist.
libpacman: Change _pacman_malloc sizeof style to use (*pointer) instead of plain structure.