Core/Entities: Readded check removed in d7460887c8, caused flying ghost players to not move if they died during a root effect, root flag was never cleared clientside and impeded movement.

(cherry picked from commit ef85d01746)

# Conflicts:
#	src/server/game/Server/WorldSession.cpp

src/server/game/Entities/Player/Player.cpp

@@ -98,6 +98,7 @@
 #include "UpdateData.h"
 #include "UpdateFieldFlags.h"
 #include "Util.h"
+#include "Vehicle.h"
 #include "VehiclePackets.h"
 #include "Weather.h"
 #include "WeatherMgr.h"
@@ -26968,6 +26969,9 @@ void Player::ValidateMovementInfo(MovementInfo* mi)
             mi->RemoveMovementFlag((maskToRemove));
     #endif
 
+    if (!GetVehicleBase() || !(GetVehicle()->GetVehicleInfo()->m_flags & VEHICLE_FLAG_FIXED_POSITION))
+        REMOVE_VIOLATING_FLAGS(mi->HasMovementFlag(MOVEMENTFLAG_ROOT), MOVEMENTFLAG_ROOT);
+
     /*! This must be a packet spoofing attempt. MOVEMENTFLAG_ROOT sent from the client is not valid
         in conjunction with any of the moving movement flags such as MOVEMENTFLAG_FORWARD.
         It will freeze clients that receive this player's movement info.

src/server/game/Entities/Vehicle/VehicleDefines.h

@@ -66,7 +66,8 @@ enum VehicleFlags
     VEHICLE_FLAG_FULLSPEEDPITCHING               = 0x00000020,           // Sets MOVEFLAG2_FULLSPEEDPITCHING
     VEHICLE_FLAG_CUSTOM_PITCH                    = 0x00000040,           // If set use pitchMin and pitchMax from DBC, otherwise pitchMin = -pi/2, pitchMax = pi/2
     VEHICLE_FLAG_ADJUST_AIM_ANGLE                = 0x00000400,           // Lua_IsVehicleAimAngleAdjustable
-    VEHICLE_FLAG_ADJUST_AIM_POWER                = 0x00000800            // Lua_IsVehicleAimPowerAdjustable
+    VEHICLE_FLAG_ADJUST_AIM_POWER                = 0x00000800,           // Lua_IsVehicleAimPowerAdjustable
+    VEHICLE_FLAG_FIXED_POSITION                  = 0x00200000            // Used for cannons, when they should be rooted
 };
 
 enum VehicleSpells