Fix OP4 grapple detection

[anzz1]

Stop creation of ladder waypoints in air while autowaypoint=1 and a player uses grapple hook in OP4

-   if(pEntity->v.movetype == MOVETYPE_FLY && players[idx].current_weapon_id == GEARBOX_WEAPON_GRAPPLE)
+   if(pEntity->v.movetype == MOVETYPE_FLY && pEntity->v.flags & FL_IMMUNE_LAVA)

Bug
The PlayerClient_Valve_CurrentWeapon function sometimes didn't correctly keep track of a player's weapon when autowaypoint=1 and this led to creation of ladder waypoints in midair while a player used the grapple hook

Fix
What the OP4 engine itself uses for ladder detection is the otherwise unused FL_IMMUNE_LAVA (0x80000) (1<<19) flag.
CGrapple.cpp#L168

void CGrapple::PrimaryAttack()
{
/* ... */
	if (m_pTip->GetGrappleType() > CGrappleTip::TargetClass::SMALL)
	{
		m_pPlayer->pev->movetype = MOVETYPE_FLY;
		//Tells the physics code that the player is not on a ladder - Solokiller
		m_pPlayer->pev->flags |= FL_IMMUNE_LAVA;
	}
/* ... */
}

pm_shared.cpp#L617

void PM_UpdateStepSound()
{
/* ... */
	const bool fLadder = pmove->movetype == MOVETYPE_FLY && (pmove->flags & FL_IMMUNE_LAVA) == 0; // IsOnLadder();
/* ... */
}

The halflife-op4-updated repo is a remake of the original OP4 dll so I did check with a decompiler that this functionality does indeed exist in the vanilla game (opfor.dll / opfor.so) and wasn't something that was added for the updated version

Artifact
Archive: jk_botti_grapple_bug.zip
Contains files: op4_bounce.bsp (the map where the bug occured) and op4_bounce.wpt + op4_bounce.matrix the bugged waypoint files
Note: You need to replace MSG_ALL:MSG_ONE with MSG_BROADCAST:MSG_ONE_UNRELIABLE in waypoint.cpp if you wish to view these ingame with show_waypoints 1 as there are so many waypoints in the file that the reliable channel will otherwise overflow.