HPCC-9135 crlf before mime boundary line should not in file content

When uploading a file, there is a crlf before mime boundary line. The
crlf is added by browser. The existing code reads and copy it as one
part of file content. This fix detects the crlf and does not copy it
into the file content.

Signed-off-by: Kevin Wang <kevin.wang@lexisnexis.com>