parser: fix if expression

vlib/compiler/tests/if_expression_test.v

@@ -0,0 +1,14 @@
+
+fn test_if_expression_precedence_false_condition(){
+	b := 10
+	c := 20
+	res := 1 + if b > c { b } else { c } + 1
+	assert res == c + 2
+}
+
+fn test_if_expression_precedence_true_condition(){
+	b := 20
+	c := 10
+	res := 1 + if b > c { b } else { c } + 1
+	assert res == b + 2
+}