[FIX] compiler: fix t-call at root of template causing crashes

Because the default content of a t-call is compiled before the block of
the t-call is created, the default content can sometimes incorrectly be
treated as though it is at the root of the template. This causes various
issues, in the case of a t-if, the default content will just replace the
t-call entirely when truthy, and when falsy the template will not return
anything, leading to a crash. Similar things occur with t-foreach and
t-out with a default content.

This commit fixes that by moving the block creation for the t-call ahead
of the compilation of the default content. In doing so, it makes the
context attribute "preventRoot" obsolete: the purpose of this attribute
is to somehow make the code aware that the root of the template will be
defined later, but because it wasn't propagated everywhere properly it
caused this issue. Now that the root already exists before we compile
the default content, we don't need it anymore.

tests/compiler/t_call.test.ts

@@ -430,6 +430,48 @@ describe("t-call (template calling)", () => {
     expect(context.renderToString("main")).toBe(expected);
   });
 
+  test("root t-call with body: t-if true", () => {
+    const context = new TestContext();
+    const subTemplate = `sub`;
+    const main = `<t t-call="subTemplate"><t t-if="true">zero</t></t>`;
+    context.addTemplate("subTemplate", subTemplate);
+    context.addTemplate("main", main);
+    const expected = "sub";
+    expect(context.renderToString("main")).toBe(expected);
+  });
+
+  test("root t-call with body: t-if false", () => {
+    const context = new TestContext();
+    const subTemplate = `sub`;
+    const main = `<t t-call="subTemplate"><t t-if="false">zero</t></t>`;
+    context.addTemplate("subTemplate", subTemplate);
+    context.addTemplate("main", main);
+    const expected = "sub";
+    expect(context.renderToString("main")).toBe(expected);
+  });
+
+  test("root t-call with body: t-out with default", () => {
+    const context = new TestContext();
+    const subTemplate = `sub`;
+    const main = `<t t-call="subTemplate"><t t-out="nothing">default</t></t>`;
+    context.addTemplate("subTemplate", subTemplate);
+    context.addTemplate("main", main);
+    const expected = "sub";
+    expect(context.renderToString("main")).toBe(expected);
+  });
+
+  test("root t-call with body: t-foreach", () => {
+    const context = new TestContext();
+    const subTemplate = `sub`;
+    const main = `<t t-call="subTemplate">
+      <t t-foreach="[1]" t-as="i" t-key="i">1</t>
+    </t>`;
+    context.addTemplate("subTemplate", subTemplate);
+    context.addTemplate("main", main);
+    const expected = "sub";
+    expect(context.renderToString("main")).toBe(expected);
+  });
+
   test("dynamic t-call", () => {
     const context = new TestContext();
     const foo = `<foo><t t-esc="val"/></foo>`;