Hi folks,

I managed to crash mandoc(1) today while formatting a manual.  Narrowed 
down:

      1	.Dd $Mdocdate$
      2	.Dt FOO 1
      3	.Os
      4	.Sh NAME
      5	.Nm foo
      6	.Nd bar
      7	.Sh DESCRIPTION
      8	The
      9	.Bl -hang
     10	.It Nm Fo o
     11	xyzzy
     12	.El

In short, the "Fo" is continuing a node subtree perpetually and the HEAD 
for the "It" on line 10 just keeps going.  There's a check for 
"n->next->child" which thus crashes because "n->next" is NULL.

The fix is very simple and enclosed.

Ok?

Best,

Kristaps