[Client] Fix manual setting of inertial force

Actors who are on the ground have their inertial force ignored, so they are now made to not be regarded as being on the ground in World::setInertialForce()

apps/openmw/mwworld/worldimp.cpp

@@ -1604,7 +1604,9 @@ namespace MWWorld
     */
     void World::setInertialForce(const Ptr& ptr, const osg::Vec3f &force)
     {
-        mPhysics->getActor(ptr)->setInertialForce(force);
+        MWPhysics::Actor *actor = mPhysics->getActor(ptr);
+        actor->setOnGround(false);
+        actor->setInertialForce(force);
     }
     /*
         End of tes3mp addition