[FIX] mail: properly suggest users to chat with

Before this commit, it was not possible to choose the user you want to
chat with in a chat window anymore. This was because the dropdown that
suggest the users appeared under the chat windows since commit
https://github.com/odoo/odoo/commit/7b965a9673a9124e6e045b8a290a156eed402ad5

Indeed, the mentioned commit changed the z-indexes so that chat windows
are still usable when a modal is opened. This was done by making the
chat windows always have the greatest z-index... forgetting this would
make them appear on top of their own autocomplete dropdowns.

This commit restores the feature while keeping the ability to talk while
a modal is opened. See code comments for details.

opw-785162

addons/mail/static/src/less/chat_window.less

@@ -3,7 +3,7 @@
 @o-mail-chatter-gap: 10px; // has to be defined here as this file is both in
                            // backend and other assets (livechat)
 @o-chat-header-height: 46px;
-@o-chat-window-zindex: 1101; // blockUI's z-index is 1100 > @zindex-modal
+@o-chat-window-zindex: @zindex-modal + 1;
 
 .o_chat_window {
     .o-flex-display();
@@ -145,6 +145,17 @@
     }
 }
 
+.o_ui_blocked .o_chat_window {
+    // We cannot put the z-index of chat windows directly to be greater than
+    // blockUI's as ui-autocomplete dropdowns (which are below blockUI) would
+    // appear under the chat windows (and ui-autocomplete is used to choose the
+    // person you want to chat with). So we only raise the z-index value when
+    // the ui is really blocked (in that case, the ui-autocomplete dropdowns
+    // will disappear under the chat windows but this is not really an issue as
+    // there should not be any at that time).
+    z-index: 1101; // blockUI's z-index is 1100
+}
+
 .o_no_chat_window .o_chat_window {
     display: none;
 }

addons/web/static/src/js/core/misc.js

@@ -59,12 +59,14 @@ function blockUI() {
     var throbber = new Throbber();
     throbbers.push(throbber);
     throbber.appendTo($(".oe_blockui_spin_container"));
+    $(document.body).addClass('o_ui_blocked');
     return tmp;
 }
 
 function unblockUI() {
     _.invoke(throbbers, 'destroy');
     throbbers = [];
+    $(document.body).removeClass('o_ui_blocked');
     return $.unblockUI.apply($, arguments);
 }