checker: fix $res() used in defer {} blocks with more statements, add a test (#22998)

vlib/v/checker/checker.v

@@ -2177,6 +2177,7 @@ fn (mut c Checker) stmt(mut node ast.Stmt) {
 			c.inside_const = false
 		}
 		ast.DeferStmt {
+			c.inside_defer = true
 			if node.idx_in_fn < 0 && c.table.cur_fn != unsafe { nil } {
 				node.idx_in_fn = c.table.cur_fn.defer_stmts.len
 				c.table.cur_fn.defer_stmts << unsafe { &node }
@@ -2203,7 +2204,6 @@ fn (mut c Checker) stmt(mut node ast.Stmt) {
 					node.defer_vars[i] = id
 				}
 			}
-			c.inside_defer = true
 			c.stmts(mut node.stmts)
 			c.inside_defer = false
 		}

vlib/v/tests/defer/defer_use_returned_value_test.v

@@ -38,3 +38,19 @@ fn test_with_multi_return() {
 	assert test.a == a
 	assert test.b == b
 }
+
+fn f() int {
+	defer {
+		a := $res()
+		assert true
+		println('result is: ${a}')
+	}
+	if true {
+		return 123
+	}
+	return 42
+}
+
+fn test_res_in_defer_blocks_with_many_statements_works() {
+	assert f() == 123
+}