Fix in tab

[maartenbreddels]

import ipyleaflet as l
import ipywidgets as widgets
widgets.Tab(
    children=[l.Map()]
)

gives in the js console:

index.es6.js:389 TypeError: Cannot read properties of undefined (reading 'invalidateSize')

``` index.es6.js:389 TypeError: Cannot read properties of undefined (reading 'invalidateSize') at ii._processLuminoMessage (Map.js:470:18) at ii.processPhosphorMessage (Map.js:442:10) at e.processMessage (widget.js:722:20) at f (index.es6.js:442:21) at Object.n [as sendMessage] (index.es6.js:178:13) at t.show (index.es6.js:1247:25) at e._onCurrentChanged (tabpanel.js:271:27) at c (index.es6.js:459:18) at e.emit (index.es6.js:416:17) at t.emit (index.es6.js:99:17) u @ index.es6.js:389 f @ index.es6.js:445 n @ index.es6.js:178 t.show @ index.es6.js:1247 e._onCurrentChanged @ tabpanel.js:271 c @ index.es6.js:459 e.emit @ index.es6.js:416 t.emit @ index.es6.js:99 e._adjustCurrentForRemove @ index.es6.js:8894 e.removeTabAt @ index.es6.js:8367 e.removeTab @ index.es6.js:8339 e._onWidgetRemoved @ tabpanel.js:304 c @ index.es6.js:459 e.emit @ index.es6.js:416 t.emit @ index.es6.js:99 e.onChildRemoved @ tabpanel.js:76 t.processMessage @ index.es6.js:1401 f @ index.es6.js:442 n @ index.es6.js:187 set @ index.es6.js:1052 t.dispose @ index.es6.js:912 (anonymous) @ widget_selectioncontainer.js:339 Promise.then (async) e.addChildView @ widget_selectioncontainer.js:330 t.update @ viewlist.js:54 e.updateTabs @ widget_selectioncontainer.js:316 e.render @ widget_selectioncontainer.js:304 (anonymous) @ manager-base.js:106 Promise.then (async) (anonymous) @ manager-base.js:100 Promise.then (async) t.create_view @ manager-base.js:99 t.display_model @ manager-base.js:86 (anonymous) @ extension.js:137 Promise.then (async) (anonymous) @ extension.js:136 (anonymous) @ extension.js:168 OutputArea.append_mime_type @ main.min.js?v=7e50cbb06bc00a057be483279bc938810b467e6c9dd9b5d91eb4b06b75704564224322da095d638da40ccb4cbe79a45d46de8eb77ac598b5c1c744d71ff0834f:59827 OutputArea.append_display_data @ main.min.js?v=7e50cbb06bc00a057be483279bc938810b467e6c9dd9b5d91eb4b06b75704564224322da095d638da40ccb4cbe79a45d46de8eb77ac598b5c1c744d71ff0834f:59788 OutputArea.append_output @ main.min.js?v=7e50cbb06bc00a057be483279bc938810b467e6c9dd9b5d91eb4b06b75704564224322da095d638da40ccb4cbe79a45d46de8eb77ac598b5c1c744d71ff0834f:59469 OutputArea.handle_output @ main.min.js?v=7e50cbb06bc00a057be483279bc938810b467e6c9dd9b5d91eb4b06b75704564224322da095d638da40ccb4cbe79a45d46de8eb77ac598b5c1c744d71ff0834f:59380 output @ main.min.js?v=7e50cbb06bc00a057be483279bc938810b467e6c9dd9b5d91eb4b06b75704564224322da095d638da40ccb4cbe79a45d46de8eb77ac598b5c1c744d71ff0834f:61213 Kernel._handle_output_message @ main.min.js?v=7e50cbb06bc00a057be483279bc938810b467e6c9dd9b5d91eb4b06b75704564224322da095d638da40ccb4cbe79a45d46de8eb77ac598b5c1c744d71ff0834f:62975 i @ main.min.js?v=7e50cbb06bc00a057be483279bc938810b467e6c9dd9b5d91eb4b06b75704564224322da095d638da40ccb4cbe79a45d46de8eb77ac598b5c1c744d71ff0834f:2 Kernel._handle_iopub_message @ main.min.js?v=7e50cbb06bc00a057be483279bc938810b467e6c9dd9b5d91eb4b06b75704564224322da095d638da40ccb4cbe79a45d46de8eb77ac598b5c1c744d71ff0834f:63015 Kernel._finish_ws_message @ main.min.js?v=7e50cbb06bc00a057be483279bc938810b467e6c9dd9b5d91eb4b06b75704564224322da095d638da40ccb4cbe79a45d46de8eb77ac598b5c1c744d71ff0834f:62794 (anonymous) @ main.min.js?v=7e50cbb06bc00a057be483279bc938810b467e6c9dd9b5d91eb4b06b75704564224322da095d638da40ccb4cbe79a45d46de8eb77ac598b5c1c744d71ff0834f:62785 Promise.then (async) Kernel._handle_ws_message @ main.min.js?v=7e50cbb06bc00a057be483279bc938810b467e6c9dd9b5d91eb4b06b75704564224322da095d638da40ccb4cbe79a45d46de8eb77ac598b5c1c744d71ff0834f:62785 i @ main.min.js?v=7e50cbb06bc00a057be483279bc938810b467e6c9dd9b5d91eb4b06b75704564224322da095d638da40ccb4cbe79a45d46de8eb77ac598b5c1c744d71ff0834f:2 ```

@jasongrout maybe this is good for you to review, as you understand better the lumino messaging system. This might also indicate a bug in jupyter-widgets.

[martinRenou]

Thanks!

[martinRenou]

Arf, let's merge and I'll fix the CI separately