When avy-goto-line called with numbered argument it tries to mimic behaviour of 'goto-line'. However, if some part of text is hidden by narrowing, avy-goto-line failed to notice for that.

How to reproduce issue:

1. Open any file, for example avy.el.
2. Go to line 1000
3. narrow to current function: M-x narrow-to-defun
4. call goto-line with argument 1000: M-x goto-line RET 1000
   Cursor staid on the same line.
5. Now call avy-goto-line with argument 1000: M-x avy-goto-line RET 1000
   Cursor moved to the end of visible text.

As you can see, behaviour of goto-line and avy-goto-line is differs.