[blockly] Fix missing event property causes JS error

[stefan-hoehn]

see https://community.openhab.org/t/blockly-proposal-to-change-contextual-info-blocks/154403/27

if (event.itemState?.toString() != undefined) {
  console.info('Event IS defined');
} else {
  console.info('Event isn\'t defined');
}
if (event.itemState !== undefined ? parseFloat(event.itemState.toString()) : undefined != undefined) {
  console.info('Event IS defined');
} else {
  console.info('Event isn\'t defined');
}
if (event.itemState !== undefined ? Quantity(event.itemState.toString() : undefined) != undefined) {
  console.info('Event IS defined');
} else {
  console.info('Event isn\'t defined');
}

[relativeci]

Job #1837: Bundle Size — 10.55MiB (~+0.01%).

7c79397(current) vs 1bebae3 main#1833(baseline)

Warning

Bundle contains 2 duplicate packages – View duplicate packages

Bundle metrics   1 change

	Current Job #1837	Baseline Job #1833
Initial JS	1.86MiB	1.86MiB
Initial CSS	607.87KiB	607.87KiB
Cache Invalidation	17.97%	18.31%
Chunks	223	223
Assets	246	246
Modules	2857	2857
Duplicate Modules	141	141
Duplicate Code	1.73%	1.73%
Packages	94	94
Duplicate Packages	2	2

Bundle size by type   1 change 1 regression

	Current Job #1837	Baseline Job #1833
JS	8.74MiB (~+0.01%)	8.74MiB
CSS	890.03KiB	890.03KiB
Fonts	526.1KiB	526.1KiB
Media	295.6KiB	295.6KiB
IMG	140.74KiB	140.74KiB
HTML	1.24KiB	1.24KiB
Other	871B	871B

---

View job #1837 report View stefan-hoehn:blockly_eventcontex... branch activity View project dashboard

[florian-h05]

Please have a look at my comments.

[florian-h05]

LGTM, thanks!