avoid uninitialised var use in nfs_serv.c error paths

avoid uninitialised var use in nfs_serv.c error paths

some functions have a nfsmout label with code that assumes NDINIT has
been called

nfsrv_rename has two NDINIT calls, the nfsmout code assumes both are
setup but is only jumped to when none/one is setup

found with llvm scan-build
checked by deraadt@ beck@, ok miod@