libvirt-domain: fix no error report when p2p migrate fail

After commit a26669d7, we only jump to error when
virDomainMigrateUnmanagedParams return a value less than -1.
this will make the migrate result always be success even we
meet some problem.

Signed-off-by: Luyao Huang <lhuang@redhat.com>

src/libvirt-domain.c

@@ -4478,7 +4478,7 @@ virDomainMigrateToURI3(virDomainPtr domain,
         dconnuri = NULL;
 
     if (virDomainMigrateUnmanagedParams(domain, dconnuri,
-                                        params, nparams, flags) < -1)
+                                        params, nparams, flags) < 0)
         goto error;
 
     return 0;