game: apply https://developer.valvesoftware.com/wiki/Weapon_Respawn_Fix patch

game/shared/hl2mp/weapon_hl2mpbase.cpp

@@ -262,13 +262,40 @@ void CWeaponHL2MPBase::FallInit( void )
 
 	SetPickupTouch();
 
-	SetThink( &CBaseCombatWeapon::FallThink );
+	SetThink( &CWeaponHL2MPBase::FallThink );
 
 	SetNextThink( gpGlobals->curtime + 0.1f );
 
 #endif
 }
 
+#ifdef GAME_DLL
+void CWeaponHL2MPBase::FallThink( void )
+{
+	// Prevent the common HL2DM weapon respawn bug from happening
+	// When a weapon is spawned, the following chain of events occurs:
+	// - Spawn() is called (duh), which then calls FallInit()
+	// - FallInit() is called, and prepares the weapon's 'Think' function (CBaseCombatWeapon::FallThink())
+	// - FallThink() is called, and performs several checks before deciding whether the weapon should Materialize()
+	// - Materialize() is called (the HL2DM version above), which sets the weapon's respawn location.
+	// The problem occurs when a weapon isn't placed properly by a level designer.
+	// If the weapon is unable to move from its location (e.g. if its bounding box is halfway inside a wall), Materialize() never gets called.
+	// Since Materialize() never gets called, the weapon's respawn location is never set, so if a person picks it up, it respawns forever at
+	// 0 0 0 on the map (infinite loop of fall, wait, respawn, not nice at all for performance and bandwidth!)
+
+	if( hasSpawnFlags( SF_NORESPAWN ) == false )
+	{
+		if( GetOriginalSpawnOrigin() == vec3_origin )
+		{
+			m_vOriginalSpawnOrigin = GetAbsOrigin();
+			m_vOriginalSpawnAngles = GetAbsAngles();
+		}
+	}
+
+	return BaseClass::FallThink();
+}
+#endif
+
 const CHL2MPSWeaponInfo &CWeaponHL2MPBase::GetHL2MPWpnData() const
 {
 	const FileWeaponInfo_t *pWeaponInfo = &GetWpnData();

game/shared/hl2mp/weapon_hl2mpbase.h

@@ -45,6 +45,7 @@ public:
 
 		void Materialize( void );
 		virtual	int ObjectCaps( void );
+		virtual	void FallThink( void );
 	#endif
 
 	// All predicted weapons need to implement and return true