[FIX] qweb: handle variable expressions in t-if

closes #390
closes #362

tests/qweb/__snapshots__/qweb.test.ts.snap

@@ -1502,6 +1502,22 @@ exports[`t-if t-esc with t-if 1`] = `
 }"
 `;
 
+exports[`t-if t-set, then t-if 1`] = `
+"function anonymous(context,extra
+) {
+    var h = this.h;
+    let c1 = [], p1 = {key:1};
+    var vn1 = h('div', p1, c1);
+    var _2 = 'test';
+    if ('test') {
+        if (_2 || _2 === 0) {
+            c1.push({text: _2});
+        }
+    }
+    return vn1;
+}"
+`;
+
 exports[`t-key can use t-key directive on a node 1`] = `
 "function anonymous(context,extra
 ) {

tests/qweb/qweb.test.ts

@@ -338,6 +338,17 @@ describe("t-if", () => {
     qweb.addTemplate("test", `<div><t t-if="false">abc</t><t t-else="1" t-esc="'x'"/></div>`);
     expect(renderToString(qweb, "test")).toBe("<div>x</div>");
   });
+
+  test("t-set, then t-if", () => {
+    qweb.addTemplate("test", `
+      <div>
+        <t t-set="title" t-value="'test'"/>
+        <t t-if="title"><t t-esc="title"/></t>
+      </div>`);
+    const result = renderToString(qweb, "test");
+    const expected = `<div>test</div>`;
+    expect(result).toBe(expected);
+  });
 });
 
 describe("attributes", () => {