Ensure that we don't reset the current page view if the user inputs an invalid page number (PR 7289 follow-up)
Ensure that we don't reset the current page view if the user inputs an invalid page number (PR 7289 follow-up)

After PR 7289, we'll now reset the current page view in cases where I don't think we should. To avoid this, this patch ensures that we'll not modify the position when the page number is out-of-bounds.

**STR:**
1. Open http://mozilla.github.io/pdf.js/web/viewer.html#page=1&zoom=auto,-98,696
2. Enter an invalid number, e.g. `1000`, in the `pageNumber` input.

**ER:**
The current position in the document shouldn't change, since the page number wasn't valid.

**AR:**
The document resets to the top of the page `1`.

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