Fix password field manipulation bugs.

[FIXED]     By stubbing the password field's document, we broke some editing capabilities. Stub the document in a way that respects its length.

platform-independent/java/gui/src/main/java/com/lyndir/masterpassword/gui/util/Components.java

@@ -212,7 +212,7 @@ public abstract class Components {
             @Override
             public String getString(final int where, final int len)
                     throws BadLocationException {
-                return "";
+                return new String( new char[this.length()] );
             }
         } ), null, 0 ) {
             {