fix error. (#372)

L 10/17/2018 - 00:39:52: [SM] Call stack trace:
L 10/17/2018 - 00:39:52: [SM]   [0] GetEntPropString
L 10/17/2018 - 00:39:52: [SM]   [1] Line 758, /home/travis/build/Bara/TroubleinTerroristTown/addons/sourcemod/scripting/include/entity.inc::GetEntityClassname
L 10/17/2018 - 00:39:52: [SM]   [2] Line 540, addons/sourcemod/scripting/ttt/ttt_c4_jihad.sp::OnPlayerRunCmd
L 10/17/2018 - 00:45:34: [SM] Exception reported: Entity -1 (-1) is invalid
L 10/17/2018 - 00:45:34: [SM] Blaming: ttt\ttt_c4_jihad.smx
L 10/17/2018 - 00:45:34: [SM] Call stack trace:

addons/sourcemod/scripting/ttt/ttt_c4_jihad.sp

@@ -534,7 +534,7 @@ public Action OnPlayerRunCmd(int client, int& buttons, int& impulse, float vel[3
     {
         int iWeapon = GetEntPropEnt(client, Prop_Send, "m_hActiveWeapon");
 
-        if (!IsValidEntity(iWeapon))
+        if (iWeapon != -1 && IsValidEdict(iWeapon))
         {
             char sWeapon[32];
             GetEntityClassname(iWeapon, sWeapon, sizeof(sWeapon));