Fix force save when pressing F4

Forgot to remove F4 from the blocked list in 5acad04 @icomrade so it was
being overwritten.

Shift + P is not a hardcoded engine bind. It is just the default
DSInterface bind, so actionKeys "DSInterface" covers that in f760896.

SQF/dayz_code/init/variables.sqf

@@ -589,6 +589,7 @@ if (!isDedicated) then {
 
 	//player special variables
 	dayz_bloodBagHumanity = 300;
+	dayz_lastCheckBit = 0;
 	dayz_lastDamageSourceNull = false;
 	dayz_lastDamageSource = "none";
 	dayz_lastDamageTime = 0;