fix: fcm task was not cancelable and cannot remove listeners

app/src/main/java/org/thoughtcrime/securesms/loki/utilities/FcmUtils.kt

@@ -0,0 +1,19 @@
+@file:JvmName("FcmUtils")
+package org.thoughtcrime.securesms.loki.utilities
+
+import com.google.android.gms.tasks.Task
+import com.google.firebase.iid.FirebaseInstanceId
+import com.google.firebase.iid.InstanceIdResult
+import kotlinx.coroutines.*
+
+
+fun getFcmInstanceId(body: (Task<InstanceIdResult>)->Unit): Job = MainScope().launch(Dispatchers.IO) {
+    val task = FirebaseInstanceId.getInstance().instanceId
+    while (!task.isComplete && isActive) {
+        // wait for task to complete while we are active
+    }
+    if (!isActive) return@launch // don't 'complete' task if we were canceled
+    withContext(Dispatchers.Main) {
+        body(task)
+    }
+}