Fixed RL11 type errors

devices/pdp11/machine/1170/panel/debugger/xxdp/README.md

@@ -32,3 +32,4 @@ we need to use an RL02 drive.  A typical PDP-11 machine with a single RL11 disk
 up to four such drives, which we refer to as RL0 through RL3.
 
 To select drive RL0, press {% include machine-command.html type='button' label='Select RL0' machine='test1170' component='RL11' command='selectDrive' value='RL0' %}
+

modules/pdp11/lib/rl11.js

@@ -39,6 +39,31 @@ if (NODE) {
     var DiskPDP11 = require("./disk");
 }
 
+/**
+ * Since the Closure Compiler treats ES6 classes as @struct rather than @dict by default,
+ * it deters us from defining named properties on our components; eg:
+ *
+ *      this['exports'] = {...}
+ *
+ * results in an error:
+ *
+ *      Cannot do '[]' access on a struct
+ *
+ * So, in order to define 'exports', we must override the @struct assumption by annotating
+ * the class as @unrestricted (or @dict).  Note that this must be done both here and in the
+ * Component class, because otherwise the Compiler won't allow us to *reference* the named
+ * property either.
+ *
+ * TODO: Consider marking ALL our classes unrestricted, because otherwise it forces us to
+ * define every single property the class uses in its constructor, which results in a fair
+ * bit of redundant initialization, since many properties aren't (and don't need to be) fully
+ * initialized until the appropriate init(), reset(), restore(), etc. function is called.
+ *
+ * The upside, however, may be that since the structure of the class is completely defined by
+ * the constructor, JavaScript engines may be able to optimize and run more efficiently.
+ *
+ * @unrestricted
+ */
 class RL11 extends Component {
     /**
      * RL11(parms)
@@ -837,7 +862,9 @@ class RL11 extends Component {
             for (var i = 0; i < nDrives; i++) {
                 if (controlDrives.options[i].innerHTML == sDrive) {
                     var iDrive = Str.parseInt(controlDrives.options[i].value, 10);
-                    return this.displayDisk(iDrive, true);
+                    if (iDrive >= 0) {
+                        return this.displayDisk(iDrive, true);
+                    }
                 }
             }
         }