Fix #8182 by adding a check for left mouse click.

[ryanstewart]

This should fix #8182 . @peterflynn can you double check?

[njx]

We should test event.which at the very beginning of the mouseup handler (so we don't do any of this logic if the original click wasn't a left click).

[njx]

Also, minor nit I just noticed: the comment above says _mouseupTimeoutId will have been set to lull. I think you meant lulz. Er, I mean null. (Also missing a space after the comma.)

[njx]

Yup, it looks like this fixes it. Reviewed with a couple of notes.

[redmunds]

FYI, this bug is getting in my way, so I copied this fix locally on Win7. I am now seeing these exceptions in console:

Uncaught TypeError: Cannot read property 'which' of undefined 

Note: I think this happens when I click again before timeout happens.

[marcelgerber]

My fix #8194 worked, but I closed it in favor of this one (Sorry for the dupe).
@ryanstewart You may just take my fix

[njx]

@redmunds Oops, you're right, it looks like it should be event.button as in @SAplayer's fix. I wonder why Ryan's fix worked for me.

@SAplayer I'll look at merging yours in a bit.

[marcelgerber]

Well, both button and which work, but according to StackOverflow (see first comment), button is better defined (because it's specific to MouseEvent).
But this fix won't work because event isn't passed further down.

[njx]

@SAplayer I don't think that's the reason - event is in the outer closure, so it should be available in the nested closure.

It's weird - I can't reproduce @redmunds' exception on Windows. I thought maybe it was a shell version thing, but it doesn't seem to happen for me in any of the versions we've been using.

Anyway, it seems clear that button is better. (I looked in CodeMirror, and it looks like it tests which first, then button, probably because different browsers have historically had different properties for this...)

[njx]

Closing in favor of #8194.