Fix bug allowing concurrent execution of jobs in the same queue.

There was an issue where a higher priority job in the same queue would
become the new most eligible job, even if the current most eligible job
was actively running.

app/src/main/java/org/thoughtcrime/securesms/jobs/FastJobStorage.kt

@@ -492,6 +492,10 @@ class FastJobStorage(private val jobDatabase: JobDatabase) : JobStorage {
   private fun placeJobInEligibleList(jobCandidate: MinimalJobSpec) {
     val existingJobInQueue = jobCandidate.queueKey?.let { mostEligibleJobForQueue[it] }
     if (existingJobInQueue != null) {
+      if (existingJobInQueue.isRunning) {
+        return
+      }
+
       if (jobCandidate.globalPriority < existingJobInQueue.globalPriority) {
         return
       }