[XrdPss] Crash when initializing on 4.7.x

[herver]

Context

• xrootd updated to 4.7.1 (also present in 4.7.0)
• Simple PSS proxy

Issue

Daemon crashes during initialization:

#1  0x00007f7cc5a3193e in strdup () from /lib64/libc.so.6
#2  0x00007f7cc6bfa94d in XrdOucPsx::SetRoot (this=0x23f6eb0, lroot=0x23f7030 "/eos/cms/tier0", rroot=rroot@entry=0x0) at /usr/src/debug/xrootd/xrootd/src/XrdOuc/XrdOucPsx.cc:779
#3  0x00007f7cc34ae338 in XrdPssSys::Configure (this=this@entry=0x7f7cc36b2580 <XrdProxy::XrdProxySS>, cfn=cfn@entry=0x23bffb0 "/etc/xrootd/xrootd-cmstzero.cfg") at /usr/src/debug/xrootd/xrootd/src/XrdPss/XrdPssConfig.cc:236
#4  0x00007f7cc34aae0a in XrdPssSys::Init (this=this@entry=0x7f7cc36b2580 <XrdProxy::XrdProxySS>, lp=<optimized out>, configfn=0x23bffb0 "/etc/xrootd/xrootd-cmstzero.cfg") at /usr/src/debug/xrootd/xrootd/src/XrdPss/XrdPss.cc:158
#5  0x00007f7cc34ab190 in XrdOssGetStorageSystem (native_oss=<optimized out>, Logger=<optimized out>, config_fn=<optimized out>, parms=<optimized out>) at /usr/src/debug/xrootd/xrootd/src/XrdPss/XrdPss.cc:120
[...]

Cause

Unitialized parameter passed to XrdOucPsx::SetRoot (https://github.com/xrootd/xrootd/blob/master/src/XrdOuc/XrdOucPsx.cc#L769), it expects 2 parameters lroot and rroot but we only pass one as can be seen here: https://github.com/xrootd/xrootd/blob/master/src/XrdPss/XrdPssConfig.cc#L236