Let panel take full height in overlay view_mode

Fixes scrollbar appearing next to spinner when logging in.

css/converse.css

@@ -11162,6 +11162,9 @@ body.converse-fullscreen {
 #conversejs.converse-overlayed .converse-svg-logo {
   height: 1em; }
 
+#conversejs.converse-overlayed #controlbox #converse-login-panel {
+  height: 100%; }
+
 #conversejs #converse-modals .set-xmpp-status {
   margin: 1em; }
   #conversejs #converse-modals .set-xmpp-status .custom-control-label {

sass/_controlbox.scss

@@ -606,4 +606,9 @@
     .converse-svg-logo {
         height: 1em;
     }
+    #controlbox {
+        #converse-login-panel {
+            height: 100%;
+        }
+    }
 }