builtin-fast-export.c: fix crash on tagged trees

If a tag object points to a tree (or another unhandled type), the commit-
pointer is left uninitialized and later dereferenced. This patch adds a
default case to the switch that issues a warning and skips the object.
Signed-off-by: NErik Faye-Lund <kusmabite@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin-fast-export.c

@@ -375,6 +375,10 @@ static void get_tags_and_duplicates(struct object_array *pending,
 			case OBJ_BLOB:
 				handle_object(tag->object.sha1);
 				continue;
+			default:
+				warning("Tag points to object of unexpected type %s, skipping.",
+					typename(tag->object.type));
+				continue;
 			}
 			break;
 		default:

t/t9301-fast-export.sh

@@ -269,9 +269,8 @@ test_expect_success 'set-up a few more tags for tag export tests' '
 '
 
 # NEEDSWORK: not just check return status, but validate the output
-# two tests commented out due to crash and thus unreliable return code
-test_expect_failure 'tree_tag'        'git fast-export tree_tag'
-test_expect_failure 'tree_tag-obj'    'git fast-export tree_tag-obj'
+test_expect_success 'tree_tag'        'git fast-export tree_tag'
+test_expect_success 'tree_tag-obj'    'git fast-export tree_tag-obj'
 test_expect_failure 'tag-obj_tag'     'git fast-export tag-obj_tag'
 test_expect_failure 'tag-obj_tag-obj' 'git fast-export tag-obj_tag-obj'