fix edge case where channel would fail to start (#1611)

ErsatzTV.Core/FFmpeg/FFmpegSegmenterService.cs

@@ -17,7 +17,24 @@ public class FFmpegSegmenterService(ILogger<FFmpegSegmenterService> logger) : IF
 
     public bool TryAddWorker(string channelNumber, IHlsSessionWorker worker)
     {
-        bool result = _sessionWorkers.TryAdd(channelNumber, worker);
+        var result = false;
+        
+        // check for worker
+        if (TryGetWorker(channelNumber, out IHlsSessionWorker existing))
+        {
+            // if worker is null, pretend we added it
+            if (existing is null)
+            {
+                result = true;
+            }
+            
+            // if worker is not null, we cannot add one (so result should stay false)
+        }
+        else
+        {
+            // worker does not exist, so try adding a null one
+            result = _sessionWorkers.TryAdd(channelNumber, worker);
+        }
         
         if (result)
         {

ErsatzTV/Controllers/IptvController.cs

@@ -142,7 +142,7 @@ public class IptvController : ControllerBase
     {
         // _logger.LogDebug("Checking for session worker for channel {Channel}", channelNumber);
 
-        if (_ffmpegSegmenterService.TryGetWorker(channelNumber, out IHlsSessionWorker worker))
+        if (_ffmpegSegmenterService.TryGetWorker(channelNumber, out IHlsSessionWorker worker) && worker is not null)
         {
             // _logger.LogDebug("Trimming playlist for channel {Channel}", channelNumber);