Improve logging heuristic for sending chunks of pieces that go missing

client.go

@@ -1087,11 +1087,15 @@ another:
 		for r := range c.PeerRequests {
 			err := cl.sendChunk(t, c, r)
 			if err != nil {
-				if t.pieceComplete(int(r.Index)) && err == io.ErrUnexpectedEOF {
-					// We had the piece, but not anymore.
-				} else {
-					log.Printf("error sending chunk %+v to peer: %s", r, err)
+				i := int(r.Index)
+				if t.pieceComplete(i) {
+					t.updatePieceCompletion(i)
+					if !t.pieceComplete(i) {
+						// We had the piece, but not anymore.
+						break another
+					}
 				}
+				log.Printf("error sending chunk %+v to peer: %s", r, err)
 				// If we failed to send a chunk, choke the peer to ensure they
 				// flush all their requests. We've probably dropped a piece,
 				// but there's no way to communicate this to the peer. If they