[iRage]

Alternate Fix
I'm aware that you can remove few lines from what is being stated in this post but SA-MP acts weird sometimes so I'm just making sure that nothing would go off the plan.

Make a public variable on top of your script.

pawn Code:

new Spawned[MAX_PLAYERS];

Add this to the following callbacks: OnPlayerConnect & OnPlayerDisconnect

pawn Code:

Spawned[playerid] = 0;

Add this to the following callbacks: OnGameModeInit, OnGameModeExit

pawn Code:

for(new i = 0; i < MAX_PLAYERS; i++)
{
    Spawned[i] = 0;
}

Add this to the following callback: OnPlayerSpawn

pawn Code:

Spawned[playerid] = 1;

Now change your code to:

pawn Code:

public OnPlayerTakeDamage(playerid, issuerid, Float: amount, weaponid)
{
    if(!Spawned[playerid])
    {
        Spawned[playerid] = 1;
    }
    else
    {
        SendClientMessage(playerid, -1, "This will get called after restart on spawn");
        //Other Code
    }
    return 1;
}