BUG: crit addvma does not work about dynacut

[xjtuwxg]

A known issue, just mark it here. Adding VMA in the middle of the process address space failed:

❯ ./criu_modified/crit/crit addvma -d simple.checkpoint.deedbeef/ -sa 0x6586a34f2000 -ea 0x6586a34f3000 -rs 1
Done
❯ sudo ../criu/criu/criu restore -j -D simple.checkpoint.deedbeef
Warn  (criu/kerndat.c:857): Stale /run/criu.kdat file
Warn  (criu/libnetlink.c:55): ERROR -95 reported by netlink
Error (criu/net.c:3155): Unable to create a veth pair: -95
Warn  (criu/net.c:3177): NSID isn't reported for network links
❯ sudo ../criu/criu/criu restore -j -D simple.checkpoint.deedbeef.bak
305441745. global 0xdeedbeef

[mahurabhi]

Replaced string append with os.path.join for BUG1
Added an exception for empty dump folders for BUG2