largefiles: omit redundant isstandin() before splitstandin()
There are many isstandin() invocations before splitstandin().
The former examines whether specified path starts with ".hglf/". The
latter returns after ".hglf/" of specified path if it starts with that
prefix, or returns None otherwise.
Therefore, value returned by splitstandin() can be used for
replacement of preceding isstandin(), and this replacement can omit
redundant string comparison after isstandin().
#require serve killdaemons
$ hg clone http://localhost:$HGPORT/ copy
abort: * (glob)
[255]
$ test -d copy
[1]
$ python "$TESTDIR/dumbhttp.py" -p $HGPORT --pid dumb.pid
$ cat dumb.pid >> $DAEMON_PIDS
$ hg clone http://localhost:$HGPORT/foo copy2
abort: HTTP Error 404: * (glob)
[255]
$ killdaemons.py