Make the toolbar buttons usable with keyboard when Page Fit is used

[calixteman]

No description provided.

[Snuffleupagus]

Sorry, but I think that there's a number of "issues" with this:

• Does the problem not apply in the same way to spacebar as well?
• This ignores the shift + Enter case, which I don't think is intended? Please note this part of the code.
• Last, but definitely not least, this is adding even more special-cases to an already somewhat complex event handler. Can you please see if it's possible to integrate this a little bit better into the existing checks, e.g. by re-factoring the code, to simplify things?

[Snuffleupagus]

While the updated patch is indeed much simpler, I do wonder if it's not catching way too many cases now?

With this patch if you click on one of the toolbar-buttons you now need to manually click on the viewer (or tab to it) in order for it to receive e.g. any keyboard-scrolling events. This is changing behaviour that's existed for years and it's likely to catch users off guard (and probably lead to bug reports).