[FIX] qweb: cascading t-call and t-raw="0"

Have a t-call having a t-raw="0"
that call is made to a template of the same form
i.e. itself as a t-call t-raw="0" structure

Before this commit, there was recursion crash
This was because the caller to which a t-raw="0" referred to
was incorrect. The caller here is the node which makes the t-call.
In particular, the caller was always set to last caller of the context

After this commit, there is no crash and this imbrication
of t-call and t-raw="0" is well rendered.
To sum up, we count the recursive calls to t-raw="0" and fetch
the caller in the context accordingly

closes #510

src/qweb/base_directives.ts

@@ -28,9 +28,12 @@ QWeb.utils.getFragment = function(str: string): DocumentFragment {
 QWeb.utils.htmlToVDOM = htmlToVDOM;
 
 function compileValueNode(value: any, node: Element, qweb: QWeb, ctx: CompilationContext) {
-  if (value === "0" && ctx.caller) {
-    qweb._compileNode(ctx.caller, ctx);
-    return;
+  if (value === "0") {
+    const caller = ctx.getCaller();
+    if (caller) {
+      qweb._compileNode(caller, ctx.getInliningContext());
+      return;
+    }
   }
 
   if (value.xml instanceof NodeList && !value.id) {