use currentUserFlow

[mahibi]

The lateinit currentUser is only set once ChatActivity's async
initData() call completes, which can race with onResume() calling
getRoom() and crash with UninitializedPropertyAccessException.

currentUserFlow is populated eagerly and independently of that init
sequencing, so use it instead - this removes the race rather than
just guarding around it.

avoids the crash

Exception in thread "main"
java.lang.RuntimeException: Unable to resume activity {com.nextcloud.talk2/com.nextcloud.talk.chat.ChatActivity}: kotlin.UninitializedPropertyAccessException: lateinit property currentUser has not been initialized
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:5695)
at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:5728)
at android.app.servertransaction.ResumeActivityItem.execute(ResumeActivityItem.java:73)
at android.app.servertransaction.ActivityTransactionItem.execute(ActivityTransactionItem.java:63)
at android.app.servertransaction.TransactionExecutor.executeLifecycleItem(TransactionExecutor.java:169)
at android.app.servertransaction.TransactionExecutor.executeTransactionItems(TransactionExecutor.java:101)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:80)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2860)
at android.os.Handler.dispatchMessage(Handler.java:110)
at android.os.Looper.loopOnce(Looper.java:283)
at android.os.Looper.loop(Looper.java:392)
at android.app.ActivityThread.main(ActivityThread.java:9248)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:611)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:944)
Caused by: kotlin.UninitializedPropertyAccessException: lateinit property currentUser has not been initialized
at com.nextcloud.talk.chat.viewmodels.ChatViewModel.getCurrentUser(ChatViewModel.kt:319)
at com.nextcloud.talk.chat.viewmodels.ChatViewModel.getRoom(ChatViewModel.kt:1740)
at com.nextcloud.talk.chat.ChatActivity.onResume(ChatActivity.kt:2043)
at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1803)
at android.app.Activity.performResume(Activity.java:9376)
at android.app.ActivityThread.performResumeActivity(ActivityThread.java:5680)
... 14 more

🏁 Checklist

• ⛑️ Tests (unit and/or integration) are included or not needed
• 🔖 Capability is checked or not needed
• 🔙 Backport requests are created or not needed: /backport to stable-xx.x
• 📅 Milestone is set
• 🌸 PR title is meaningful (if it should be in the changelog: is it meaningful to users?)

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI

[github-actions]

📱 QA build

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Commit	2946d5f
Version	6741
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