fix writing of message (forgot to increment offset)

StackExchange.Redis/StackExchange/Redis/PhysicalConnection.cs

@@ -637,7 +637,8 @@ private static int WriteUnified(Span<byte> span, byte[] value, int offset = 0)
             else
             {
                 offset = WriteRaw(span, value.Length, offset: offset);
-                new ReadOnlySpan<byte>(value).CopyTo(span.Slice(offset));
+                new ReadOnlySpan<byte>(value).CopyTo(span.Slice(offset, value.Length));
+                offset += value.Length;
                 offset = WriteCrlf(span, offset);
             }
             return offset;