improve playout error formatting (#2477)

ErsatzTV.Application/Playouts/Commands/BuildPlayoutHandler.cs

@@ -300,6 +300,14 @@ public class BuildPlayoutHandler : IRequestHandler<BuildPlayout, Either<BaseErro
             return BaseError.New(
                 $"Timeout building playout for channel {channelName}; this may be a bug!");
         }
+        catch (PlayoutBuildException ex)
+        {
+            newBuildStatus.Success = false;
+            newBuildStatus.Message = ex.Message;
+
+            return BaseError.New(
+                $"Unexpected error building playout for channel {channelName}: {ex.Message}");
+        }
         catch (Exception ex)
         {
             DebugBreak.Break();