Null pointer deref in getdirentries()

UP machine running 6.0.  This machine does lots of unmounting, so it's
possible rm raced with the umount.

Fatal trap 12: page fault while in kernel mode
fault virtual address   = 0x7b
fault code              = supervisor read, page not present
instruction pointer     = 0x20:0xc055d705
stack pointer           = 0x28:0xe766bc3c
frame pointer           = 0x28:0xe766bcd4
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 59277 (rm)

db> wh
Tracing pid 59277 tid 100059 td 0xc6201180
getdirentries(c6201180,e766bd04,10,418,4) at getdirentries+0x75
syscall(c068003b,3b,3b,8050000,805a300) at syscall+0x2c0
Xint0x80_syscall() at Xint0x80_syscall+0x1f
--- syscall (196, FreeBSD ELF32, getdirentries), eip = 0x280bec6f, esp = 0xbfbfeb6c, ebp = 0xbfbfeb98 ---

Core available.

Kris