[HL2MP] Fix grenade ownership

[speedvoltage]

Issue When player 1 holds a frag grenade in their physcannon and player 2 punts the frag grenade that player 1 is still holding, it resets the grenade's timer and switches the ownership to player 2.

Fix: Prevent ownership from ever being transferred for as long as a player is holding a frag grenade with their physcannon and prevent any other player from ever punting the frag grenade of another player.