cgen: fix if_expr of multi-stmts optional (#9039)

vlib/v/gen/c/cgen.v

@@ -937,6 +937,9 @@ fn (mut g Gen) stmts_with_tmp_var(stmts []ast.Stmt, tmp_var string) {
 			}
 		} else {
 			g.stmt(stmt)
+			if g.inside_if_optional && stmt is ast.ExprStmt {
+				g.writeln(';')
+			}
 		}
 		g.skip_stmt_pos = false
 		if g.inside_ternary > 0 && i < stmts.len - 1 {

vlib/v/tests/if_expr_of_optional_test.v

@@ -23,3 +23,23 @@ fn test_if_expr_of_optional() {
 	println(a3)
 	assert a3 == 2
 }
+
+fn foo_complex() ?int {
+	a := 2
+	return if a > 1 {
+		mut b := 1
+		b *= 10
+		b
+	} else {
+		mut c := 0
+		c += 2
+		println(c)
+		none
+	}
+}
+
+fn test_if_expr_of_optional_complex() {
+	a := foo_complex() or { panic('error') }
+	println(a)
+	assert a == 10
+}