tag: allow the tagger field to be missing when parsing tags

Instead of bailing out with an error, this sets tagger to NULL when
the field is missing from the object.

This makes it possible to inspect tags like this one:

http://git.kernel.org/?p=git/git.git;a=tag;h=f25a265a342aed6041ab0cc484224d9ca54b6f41

src/tag.c

@@ -122,12 +122,16 @@ static int parse_tag_buffer(git_tag *tag, const char *buffer, const char *buffer
 
 	buffer = search + 1;
 
+	tag->tagger = NULL;
+	if (*buffer != '\n') {
 		tag->tagger = git__malloc(sizeof(git_signature));
 		if (tag->tagger == NULL)
 			return GIT_ENOMEM;
 
-	if ((error = git_signature__parse(tag->tagger, &buffer, buffer_end, "tagger ", '\n')) != 0)
+		if ((error = git_signature__parse(tag->tagger, &buffer, buffer_end, "tagger ", '\n') != 0)) {
 			return git__rethrow(error, "Failed to parse tag");
+		}
+	}
 
 	if( *buffer != '\n' )
 		return git__throw(GIT_EOBJCORRUPTED, "Failed to parse tag. No new line before message");

tests/t08-tag.c

@@ -31,6 +31,7 @@ static const char *tag1_id = "b25fa35b38051e4ae45d4222e795f9df2e43f1d1";
 static const char *tag2_id = "7b4384978d2493e851f9cca7858815fac9b10980";
 static const char *tagged_commit = "e90810b8df3e80c413d903f631643c716887138d";
 static const char *bad_tag_id = "eda9f45a2a98d4c17a09d681d88569fa4ea91755";
+static const char *badly_tagged_commit = "e90810b8df3e80c413d903f631643c716887138d";
 
 BEGIN_TEST(read0, "read and parse a tag from the repository")
 	git_repository *repo;
@@ -112,13 +113,28 @@ END_TEST
 BEGIN_TEST(read3, "read and parse a tag without a tagger field")
 	git_repository *repo;
 	git_tag *bad_tag;
-	git_oid id;
+	git_commit *commit;
+	git_oid id, id_commit;
 
 	must_pass(git_repository_open(&repo, BAD_TAG_REPOSITORY_FOLDER));
 
 	git_oid_fromstr(&id, bad_tag_id);
+	git_oid_fromstr(&id_commit, badly_tagged_commit);
+
+	must_pass(git_tag_lookup(&bad_tag, repo, &id));
+	must_be_true(bad_tag != NULL);
+
+	must_be_true(strcmp(git_tag_name(bad_tag), "e90810b") == 0);
+	must_be_true(git_oid_cmp(&id, git_tag_id(bad_tag)) == 0);
+	must_be_true(bad_tag->tagger == NULL);
+
+	must_pass(git_tag_target((git_object **)&commit, bad_tag));
+	must_be_true(commit != NULL);
+
+	must_be_true(git_oid_cmp(&id_commit, git_commit_id(commit)) == 0);
 
-	must_fail(git_tag_lookup(&bad_tag, repo, &id));
+	git_tag_close(bad_tag);
+	git_commit_close(commit);
 
 	git_repository_free(repo);
 END_TEST