python: Fix comparison between signed and unsigned integer
    
    Fix these warnings, seen in python 3 builds on Travis:
    
    sanlock.c:1002:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             if (res->lver == -1) {
                           ^
    sanlock.c:1118:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
             if (res->lver == -1) {
    
    Signed-off-by: Nir Soffer <nsoffer@redhat.com>