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

[Christoph Scholtes <cschol2112@googlemail.com>]

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