improved exception message when backpressure does not leave room for the producer to call MoveNext()

Author: Mpdreamz

src/Nest/Document/Multiple/Reindex/ReindexObservable.cs

@@ -133,7 +133,7 @@ private ProducerConsumerBackPressure CreateBackPressure(IBulkAllRequest<IHitMeta
 
 			var funnelExact = producerBandwidth == bulkSize;
 			if (funnelExact)
-				throw new Exception("The back pressure settings are too conservative it provides enough documents for a single bulk but not enough room to advance "
+				throw new Exception("The back pressure settings are too conservative. They provide enough documents for a single bulk but not enough room to advance "
 					+ $"searchSize:{searchSize} * maxConcurrency:{maxConcurrency} * backPressureFactor:{backPressureFactor} = {producerBandwidth}"
 					+ $" which is exactly the bulkSize:{bulkSize}. Increase the BulkAll max concurrency or the backPressureFactor"
 				);
@@ -242,4 +242,4 @@ public void Dispose()
 			this._compositeCancelTokenSource?.Cancel();
 		}
 	}
-}
+}