seeall can trap is window closed before scan completes

[Steven Levine]

If the seeall window is closed while the initial scan is in progress, it can trap in FindAllThread or a subroutine of FindAllThread. This occurs because WM_DESTROY frees memory that the thread will attempt to access. The trap is typically in xrealloc, but it can be elsewhere.

Note that this defect may occur for other threads with similar logic.

[Steven Levine]

Fixed by changeset #1559. FindAllThread was not honoring stop request quickly and, stupidly, the semaphore request was not checked for failures. This allowed memory to be freed while the FindAllThread was still accessing it.

FindAllThread now quits quickly and these semaphore requests in the code path are checked. More checking would be better.