patch_parse: fix parsing patches only containing exact renames

Patches which contain exact renames only will not contain an actual diff
body, but only a list of files that were renamed. Thus, the patch header
is immediately followed by the terminating sequence "-- ". We currently
do not recognize this character sequence as a possible terminating
sequence. Add it and create a test to catch the failure.

src/patch_parse.c

@@ -439,6 +439,7 @@ static const parse_header_transition transitions[] = {
 	/* Next patch */
 	{ "diff --git "         , STATE_END,        0,                NULL },
 	{ "@@ -"                , STATE_END,        0,                NULL },
+	{ "-- "                 , STATE_END,        0,                NULL },
 };
 
 static int parse_header_git(

tests/diff/parse.c

@@ -57,6 +57,27 @@ static void test_parse_invalid_diff(const char *invalid_diff)
 	git_buf_free(&buf);
 }
 
+void test_diff_parse__exact_rename(void)
+{
+	const char *content =
+	    "---\n"
+	    " old_name.c => new_name.c | 0\n"
+	    " 1 file changed, 0 insertions(+), 0 deletions(-)\n"
+	    " rename old_name.c => new_name.c  (100%)\n"
+	    "\n"
+	    "diff --git a/old_name.c b/new_name.c\n"
+	    "similarity index 100%\n"
+	    "rename from old_name.c\n"
+	    "rename to new_name.c\n"
+	    "-- \n"
+	    "2.9.3\n";
+	git_diff *diff;
+
+	cl_git_pass(git_diff_from_buffer(
+		&diff, content, strlen(content)));
+	git_diff_free(diff);
+}
+
 void test_diff_parse__invalid_patches_fails(void)
 {
 	test_parse_invalid_diff(PATCH_CORRUPT_MISSING_NEW_FILE);