cgen: fix fn()? return

vlib/os/os.v

@@ -667,7 +667,7 @@ pub fn rmdir_recursive(path string) {
 pub fn rmdir_all(path string) ? {
 	mut ret_err := ''
 	items := os.ls(path) or {
-		return none
+		return error(err)
 	}
 	for item in items {
 		if os.is_dir(os.join_path(path, item)) {

vlib/v/parser/fn.v

@@ -269,6 +269,11 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 	body_start_pos := p.peek_tok.position()
 	if p.tok.kind == .lcbr {
 		stmts = p.parse_block_no_scope(true)
+		// Add return if `fn(...) ? {...}` have no return at end
+        if return_type != table.void_type && p.table.get_type_symbol(return_type).kind == .void &&
+                return_type.has_flag(.optional) && (stmts.len == 0 || stmts[stmts.len-1] !is ast.Return) {
+            stmts << ast.Return{ pos: p.tok.position() }
+        }
 	}
 	p.close_scope()
 	if !no_body && are_args_type_only {