Don't throw errors on no-argument commands

- engage
^ should not throw an error.

src/main/java/net/aufdemrand/denizen/scripts/ScriptEntry.java

@@ -128,6 +128,7 @@ else if (command.charAt(0) == '~') {
             this.pre_tagged_args = Arrays.asList(arguments);
         } else {
             this.args = new ArrayList<String>();
+            this.pre_tagged_args = new ArrayList<String>();
         }
 
         // Check for replaceable tags. We'll try not to make a habit of checking for tags/doing