compiler: fix check restricted names in for..in statement

vlib/compiler/for.v

@@ -129,6 +129,7 @@ fn (p mut Parser) for_st() {
 	}
 	// `for val in vals`
 	else if p.peek() == .key_in || p.peek() == .left_arrow {
+		p.check_not_reserved()
 		val := p.check_name()
 		p.fspace()
 		//p.check(.key_in)