XrdHttp: Corrected regression where no performance markers were sent to the client during a HTTP TPC transfer

[ccaffy]

Before this fix, no performance markers were sent to the client after a HTTP TPC transfer was started, there were weird numbers instead:

> COPY /tmp/BIGFILE_10GB HTTP/1.1
> User-Agent: curl/7.29.0
> Host: machine.cern.ch:1096
> Accept: */*
> Destination: https://machine.cern.ch:2001/tmp/BIGFILE_10GB_COPY
>
< HTTP/1.1 201 Created
< Connection: Keep-Alive
< Server: XrootD/v5.2.0-99-osghotfix...687
< Content-Type: text/plain
< Transfer-Encoding: chunked
< 

9b

9c

9c

32

0

After the fix, the perf markers are back:

> COPY /tmp/BIGFILE_10GB HTTP/1.1
> User-Agent: curl/7.29.0
> Host: machine.cern.ch:1096
> Accept: */*
> Destination: https://machine.cern.ch:2001/tmp/BIGFILE_10GB_COPY
> 
< HTTP/1.1 201 Created
< Connection: Keep-Alive
< Server: XrootD/v5.2.0-99-osghotfix...687
< Content-Type: text/plain
< Transfer-Encoding: chunked
< 
Perf Marker
Timestamp: 1685106809
Stripe Index: 0
Stripe Bytes Transferred: 0
Total Stripe Count: 1
End
Perf Marker
Timestamp: 1685106814
Stripe Index: 0
Stripe Bytes Transferred: 1017184256
Total Stripe Count: 1
RemoteConnections: tcp:137.138.123.14:2001
End
Perf Marker
Timestamp: 1685106819
Stripe Index: 0
Stripe Bytes Transferred: 2326478848
Total Stripe Count: 1
RemoteConnections: tcp:137.138.123.14:2001
End

Fixes the regression introduced in 56b2bde

[ccaffy]

@bbockelm I cannot add you as a reviewer, as I touched your code, can you please review what I did in case?

Thanks in advance !

[amadio]

Looks good to me.