fix(android): Cancel works, because lastDetail is now written

It was introduced with two readers and no writer. Cancel called
renderDetail(null), which threw on d.rows and did nothing at all - and
editDone, which uses it to hand control back after a refusal, was dead the
same way. That is why the successive fixes for "Cancel does not respond"
changed nothing: they all ended in the same silent throw.

Assigned where a detail is drawn, which is the one place that knows it.

android-client/web/app.html

@@ -586,9 +586,17 @@ document.getElementById('qx').addEventListener('click', function () {
 var detailRows = [];
 // Le dernier detail recu, pour redessiner la ligne apres une annulation sans
 // avoir a le redemander a Delphi.
+//
+// IL FAUT L'ECRIRE. Il a ete introduit avec ses deux lecteurs et aucun
+// ecrivain : Cancel appelait donc renderDetail(null), qui levait sur d.rows et
+// ne faisait rien du tout. editDone, qui s'en sert aussi pour rendre la main
+// apres un refus, etait mort de la meme facon - ce qui explique pourquoi les
+// corrections successives de "Cancel ne repond pas" n'y changeaient rien.
 var lastDetail = null;
 
 function renderDetail(d) {
+  if (!d) return;
+  lastDetail = d;
   detailRows = d.rows || [];
   document.getElementById('dtitle').textContent = d.title || '';
   var html = '', i;