fix: safeguard workspace hash computation in telemetry service

[fbricon]

Telemetry fails to initialize when starting without a workspace folder, e.g. after triggering the "Java: Add Java Runtime" command:

rejected promise not handled within 1 second: TypeError: Cannot read properties of undefined (reading 'map')
extensionHostProcess.js:204
stack trace: TypeError: Cannot read properties of undefined (reading 'map')
	at Object.<anonymous> (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:96860:85)
	at Generator.next (<anonymous>)
	at /Users/fbricon/Dev/projects/vscode-java/dist/extension.js:96830:71
	at new Promise (<anonymous>)
	at __webpack_modules__../src/telemetry.ts.__awaiter (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:96826:12)
	at Object.startTelemetry (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:96856:16)
	at /Users/fbricon/Dev/projects/vscode-java/dist/extension.js:88878:31
	at Generator.next (<anonymous>)
	at fulfilled (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:88712:58)
extensionHostProcess.js:204
rejected promise not handled within 1 second: Error: The telemetry service for vscode-java has not been started yet
extensionHostProcess.js:204
stack trace: Error: The telemetry service for vscode-java has not been started yet
	at Object.<anonymous> (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:96881:23)
	at Generator.next (<anonymous>)
	at /Users/fbricon/Dev/projects/vscode-java/dist/extension.js:96830:71
	at new Promise (<anonymous>)
	at __webpack_modules__../src/telemetry.ts.__awaiter (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:96826:12)
	at Object.sendTelemetry (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:96879:16)
	at StandardLanguageClient.<anonymous> (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:95999:45)
	at Generator.next (<anonymous>)
	at /Users/fbricon/Dev/projects/vscode-java/dist/extension.js:95629:71
	at new Promise (<anonymous>)
	at __webpack_modules__../src/standardLanguageClient.ts.__awaiter (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:95625:12)
	at /Users/fbricon/Dev/projects/vscode-java/dist/extension.js:95994:48
	at CallbackList.invoke (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:99523:39)
	at Emitter.fire (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:99585:36)
	at /Users/fbricon/Dev/projects/vscode-java/dist/extension.js:102415:40
	at handleNotification (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:98858:25)
	at handleMessage (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:98560:13)
	at processMessageQueue (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:98580:17)
	at Immediate.<anonymous> (/Users/fbricon/Dev/projects/vscode-java/dist/extension.js:98552:13)
	at process.processImmediate (node:internal/timers:485:21)
	at process.callbackTrampoline (node:internal/async_hooks:130:17)
extensionHostProcess.js:204

[datho7561]

When I try to open a single file instead of a file, VS Code is completely blank, with only the background colour. Until I can figure out why, I can't really review this PR well. I'll try to get to this tomorrow.