util.signal: Fix signalfd closure on non-Linux systems The loop was incorrect for 0-indexed arrays. It started at signalfd_num, which is the total number of signalfds, and decremented to 1 (condition was >0). So if 1 signalfd was registered, it would check only signalfds[1]. At capacity (32 signalfds) it would read past the end of the array. In every case, it would always skip the entry at position [0], leading to a leak. The swap-with-tail removal of the matched item used the post-decrement operator, leading to accessing the array slot just beyond the tail. Finally, it didn't break after finding a match. Probably harmless, but there isn't expected to be more than a single entry per fd, as far as I can tell.