tapestat: prevent reallocing to 0 bytes

Ensure that realloc is not using 0 as new size in
tape_check_tapes_and_realloc() function.

tapestat.c

@@ -200,7 +200,7 @@ void tape_check_tapes_and_realloc(void)
  /* Count again number of tapes */
  new_max_tape_drives = get_max_tape_drives();
 
- if (new_max_tape_drives > max_tape_drives) {
+ if (new_max_tape_drives > max_tape_drives && new_max_tape_drives > 0) {
  /* New tapes found: Realloc structures */
  struct tape_stats *tape_old_stats_t = (struct tape_stats *)
  realloc(tape_old_stats, sizeof(struct tape_stats) * new_max_tape_drives);