bug#12007: 24.1.50; Crash in auto-revert-handler

[Christoph Scholtes]

bzr r109196 still crashes after sitting for a while.

Same root cause as the initial report:

#1  0x0114ee85 in w32_abort () at w32fns.c:7183
        button = 6
#2  0x01041e8c in die (
    msg=0x152e13c "assertion failed: buffer->base_buffer->indirections 
 > 0",
    file=0x152c914 "buffer.c", line=1442) at alloc.c:6719
No locals.
#3  0x010a9597 in compact_buffer (buffer=0x10942400) at buffer.c:1442
No locals.
#4  0x0103f0d6 in Fgarbage_collect () at alloc.c:5434
        bind = 0x10942400
        nextb = 0x10942400
        stack_top_variable = 1 '\001'
        i = 56401306
        message_p = 8971860
        total = {1979253324, 8971752, 16938822, 56693530, 16, 16, 
1971679635,
          -284876796, 56346650, 8971784, 16939565}
        count = 18
        t1 = {
          tv_sec = 56453122,
          tv_nsec = 0
        }
#5  0x010dc545 in maybe_gc () at lisp.h:3449