shortest: don't include nullid in disambigution revset

As noted by Yuya in the review of D4118, the fact that the nodetree
always contains the nullid is not what we want for the disambiguation
case. It's not what the pure version of the code does.

Note that the updated test also passes before this patch, but it
wouldn't have passed in native-code mode once we start using the
nodetree for disambiguating nodeid prefixes.

Differential Revision: https://phab.mercurial-scm.org/D4163

mercurial/cext/revlog.c

@@ -1075,10 +1075,6 b' static int nt_init(nodetree *self, index'
 		return -1;
 	}
 	self->length = 1;
-	if (nt_insert(self, nullid, -1) == -1) {
-		free(self->nodes);
-		return -1;
-	}
 	return 0;
 }
 
@@ -1152,6 +1148,11 b' static int index_init_nt(indexObject *se'
 			self->nt = NULL;
 			return -1;
 		}
+		if (nt_insert(self->nt, nullid, -1) == -1) {
+			PyMem_Free(self->nt);
+			self->nt = NULL;
+			return -1;
+		}
 		self->ntrev = (int)index_length(self);
 		self->ntlookups = 1;
 		self->ntmisses = 0;

tests/test-revisions.t

@@ -3,7 +3,7 b''
 
   $ echo 0 > a
   $ hg ci -qAm 0
-  $ for i in 5 8 14 43; do
+  $ for i in 5 8 14 43 167; do
   >   hg up -q 0
   >   echo $i > a
   >   hg ci -qm $i
@@ -14,6 +14,7 b''
   > EOF
 
   $ hg l
+  5:00f
   4:7ba5d
   3:7ba57
   2:72
@@ -21,9 +22,10 b''
   0:b
   $ cat <<EOF >> .hg/hgrc
   > [experimental]
-  > revisions.disambiguatewithin=:3
+  > revisions.disambiguatewithin=not 4
   > EOF
   $ hg l
+  5:0
   4:7ba5d
   3:7b
   2:72