[FIX] qweb: t-esc inside t-call using outside t-set

Before this commit, the generated code was incorrect, and crashed,
when there was a t-esc="abc" in a subtemplate, with t-set="abc"
done outside the subtemplate, with syntax <t t-set="abc">value</t>.

src/qweb/base_directives.ts

@@ -49,6 +49,7 @@ function compileValueNode(value: any, node: Element, qweb: QWeb, ctx: Compilatio
   if (ctx.escaping) {
     let protectID;
     if (value.hasBody) {
+      ctx.rootContext.shouldDefineUtils = true;
       protectID = ctx.startProtectScope();
       ctx.addLine(
         `${exprID} = ${exprID} instanceof utils.VDomArray ? utils.vDomToString(${exprID}) : ${exprID};`