libxl: Fix libxlDomainPMSuspendForDuration domain active check

virDomainObjCheckActive() returns -1 if domain is not active, not 0.

Fixes cb50436c "libxl: implement virDomainPM* functions"
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>
Signed-off-by: NMarek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

src/libxl/libxl_driver.c

@@ -1459,7 +1459,7 @@ libxlDomainPMSuspendForDuration(virDomainPtr dom,
     if (libxlDomainObjBeginJob(driver, vm, LIBXL_JOB_MODIFY) < 0)
         goto cleanup;
 
-    if (!virDomainObjCheckActive(vm))
+    if (virDomainObjCheckActive(vm) < 0)
         goto endjob;
 
     /* Unlock virDomainObjPtr to not deadlock with even handler, which will try