Handle getting out-of-bounds bits in get_bit

The binary state is not padded with zeroes, so they must be inferred.

mesecons/util.lua

@@ -163,8 +163,13 @@ function mesecon.getbinstate(nodename, states)
 end
 
 function mesecon.get_bit(binary,bit)
-	bit = bit or 1
-	local c = binary:len()-(bit-1)
+	local len = binary:len()
+	if bit then
+		if bit > len then return false end
+	else
+		bit = 1
+	end
+	local c = len-(bit-1)
 	return binary:sub(c,c) == "1"
 end