Update isImmediate check

Updated to only return true for integers.

yaict.pl

@@ -132,7 +132,7 @@ sub parseOpcodeAndParams
 # Parameter is considered Position mode if it's prefixed with "0d"
 sub isImmediate
 {
-    return !(shift =~ /^0d/);
+    return shift =~ /^-?\d+$/;
 }
 
 # Check if a parameter