src/filemanager/find.c: cleanup -Wformat-signedness warning.

src/filemanager/find.c: cleanup -Wformat-signedness warning.

find.c: In function 'found_num_update':
find.c:373:44: error: format '%ld' expects argument of type 'long int', but argument 4 has type 'long unsigned int' [-Werror=format=]
     g_snprintf (buffer, sizeof (buffer), _("Found: %ld"), matches);
                                            ^

find.c: In function 'do_search':
find.c:1306:51: error: format '%zd' expects argument of type 'signed size_t', but argument 4 has type 'size_t {aka long unsigned int}' [-Werror=format=]
                                                   "Finished (ignored %zd directories)",
                                                   ^
find.c:1305:51: error: format '%zd' expects argument of type 'signed size_t', but argument 4 has type 'size_t {aka long unsigned int}' [-Werror=format=]
                                         ngettext ("Finished (ignored %zd directory)",
                                                   ^

file.c:2526:41: error: format '%zd' expects argument of type 'signed size_t', but argument 3 has type 'size_t {aka long unsigned int}' [-Werror=format=]
     label_set_textv (dsm->count_size, _("Directories: %zd, total size: %s"),
                                         ^

Signed-off-by: Andreas Mohr <and@gmx.li>
Signed-off-by: Andrew Borodin <aborodin@vmail.ru>