list-objects.c: handle unexpected non-blob entries

Fix one of the cases described in the previous commit where a tree-entry
that is promised to a blob is in fact a non-blob.

When 'lookup_blob()' returns NULL, it is because Git has cached the
requested object as a non-blob. In this case, prevent a SIGSEGV by
'die()'-ing immediately before attempting to dereference the result.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: ttaylorr

list-objects.c

@@ -133,6 +133,11 @@ static void process_tree_contents(struct traversal_context *ctx,
 					base, entry.path);
 		else {
 			struct blob *b = lookup_blob(ctx->revs->repo, &entry.oid);
+			if (!b) {
+				die(_("entry '%s' in tree %s has blob mode, "
+				      "but is not a blob"),
+				    entry.path, oid_to_hex(&tree->object.oid));
+			}
 			b->object.flags |= NOT_USER_GIVEN;
 			process_blob(ctx, b, base, entry.path);
 		}

t/t6102-rev-list-unexpected-objects.sh

@@ -20,8 +20,9 @@ test_expect_failure 'traverse unexpected non-blob entry (lone)' '
 	test_must_fail git rev-list --objects $broken_tree
 '
 
-test_expect_failure 'traverse unexpected non-blob entry (seen)' '
-	test_must_fail git rev-list --objects $tree $broken_tree
+test_expect_success 'traverse unexpected non-blob entry (seen)' '
+	test_must_fail git rev-list --objects $tree $broken_tree >output 2>&1 &&
+	test_i18ngrep "is not a blob" output
 '
 
 test_expect_success 'setup unexpected non-tree entry' '