demos/mobileGallery: harmless exception when double-touching or double-clicking the "Back" button

[Adrian Vasiliu]

1. Launch demos/mobileGallery/demo.html in any browser (including desktop).
2. If testing on desktop, reduce the width of the window such that it only shows the list of demo views (thus, making appear a "Back" button in the heading of each demo view).
3. Select any demo view (say, "Buttons").
4. *Double*-click or *double*-touch the "Back" button

=> The JavaScript console shows an error such as (depending on browser):

Uncaught TypeError: Cannot read property 'to' of undefined

or

TypeError: Result of expression 'navRecord' [undefined] is not an object

This is a minor bug in mobileGallery's code (apparently harmless).

[Adrian Vasiliu]

Avoid exception when double-clicking/touching Back button - Adrian Vasiliu (IBM, CCLA)

[cjolif]

In [30430]:

fixes #16565. Avoid exception when double-clicking/touching Back button. Thanks Adrian Vasiliu (IBM, CCLA). !strict.