virt-login-shell: correctly calculate string length
virt-login-shell: correctly calculate string length

virLoginShellGetShellArgv was not dereferencing the pointer
to the string list containing the shell parameters from the
config file, thus setting some random number as shargvlen.

Signed-off-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>
Fixes: 740e4d705284ba0598258291c2656f50075486f0
Reviewed-by: Martin Kletzander <e82f23e74d43760279ebcc505dac4ae70d5627d0@redhat.com>

crobinso/libvirt,crobinso/libvirt,zippy2/libvirt,nertpinx/libvirt,jardasgit/libvirt,jardasgit/libvirt,jardasgit/libvirt,libvirt/libvirt,nertpinx/libvirt,jardasgit/libvirt,nertpinx/libvirt,jfehlig/libvirt,zippy2/libvirt,olafhering/libvirt,jardasgit/libvirt,olafhering/libvirt,olafhering/libvirt,zippy2/libvirt,libvirt/libvirt,jfehlig/libvirt,nertpinx/libvirt,jfehlig/libvirt,nertpinx/libvirt,crobinso/libvirt,olafhering/libvirt,jfehlig/libvirt,crobinso/libvirt,libvirt/libvirt,libvirt/libvirt,zippy2/libvirt