Fix exception when rotate page without a document

[xlc]

Fixes #6438

This also fixes the exception when click Rotate Clockwise/Counterclockwise buttons in the menu.

There is still exception thrown after 30s
Uncaught TypeError: Cannot read property 'cleanup' of null
and it is tracked by #6440

[timvandermeij]

This patch seems reasonable to me. The only thing that may be a problem is that scrollPageIntoView is called a lot of times when scrolling as far as I know, so I'm not sure if this check would have any performance impact. What do others think?

[yurydelendik]

Thank you for the patch.

... if this check would have any performance impact.

The impact will be negligible -- it is called a lot, however it's not in a tight/hot loop.

[Snuffleupagus]

The only thing that may be a problem is that scrollPageIntoView is called a lot of times when scrolling as far as I know,

@timvandermeij I wonder if you're perhaps thinking of the PDFViewer_scrollUpdate method, which is called whenever scrolling occurs, through the watchScroll function.

scrollPageIntoView, on the other hand, should only be called when the page changes, e.g through the user: clicking on the previous/next buttons in the UI, using the keyboard to change page (P, N, ...), or when clicking on an internal link.
Hence I wouldn't expect scrollPageIntoView to be a particularly hot method, quite the opposite :-)

[timvandermeij]

You are right, I was confused here. Thanks for the clarification!