When an alignment with a very long sequence name/ID is opened, the alignment can't be seen

Observed when helping Javier with a very large alignment file.
Opening the file seemed to show a blank alignment. This had been an expected possibility because the alignment might have contained large areas of gaps. Only shortish sequence IDs were currently visible so there was a large whitespace where the alignment would have been expected.
However, what had actually happened is that one sequence name/ID was very long and had pushed the alignment viewport to the very right of the alignment frame. So far to the right that the two vertical grey lines by the top ruler were just off view (this was the clue to what had happened).
Fortunately the margin handle (the grey lines) could still be grabbed and dragged.

Fix: Apply the max limit (frame width minus a bit) to the width of the ID panel when opening.