parser: fix error for fn with type only argument (fix #13704) (#13709)

Author: yuyi98

vlib/v/parser/fn.v

@@ -736,7 +736,8 @@ fn (mut p Parser) fn_args() ([]ast.Param, bool, bool) {
 		|| (p.peek_tok.kind == .comma && p.table.known_type(argname))
 		|| p.peek_tok.kind == .dot || p.peek_tok.kind == .rpar
 		|| (p.tok.kind == .key_mut && (p.peek_token(2).kind == .comma
-		|| p.peek_token(2).kind == .rpar))
+		|| p.peek_token(2).kind == .rpar || (p.peek_token(1).kind == .name
+		&& p.peek_token(2).kind == .dot)))
 	// TODO copy pasta, merge 2 branches
 	if types_only {
 		mut arg_no := 1

vlib/v/tests/fn_type_only_argument_test.v

@@ -0,0 +1,16 @@
+module main
+
+import time
+
+struct Game {
+	update fn (mut time.Time) = fn (mut time time.Time) {}
+	draw   fn (mut time.Time) = fn (mut time time.Time) {}
+mut:
+	time time.Time
+}
+
+fn test_fn_type_only_argument() {
+	mut game := Game{}
+	game.time = time.Time{}
+	assert true
+}