Improve error handling in InputStream.close() for SFTP channels

[stsiano]

For most _sendClose() calls in ChannelSFftp the errors are handled just fine. However there is one exception:
When an exception is happening in the close() method of the anonymous InputStream() implementation in
https://github.com/mwiede/jsch/blob/master/src/main/java/com/jcraft/jsch/ChannelSftp.java#L1497
the Exception that was causing the error will be swallowed and replaced by an IOException with the error text "error".

This makes error analysis really difficult in these cases. Is it possible to preserve the original exception somehow (as in all the other calls of _sendClose()?