Of course BvO's workaround is a nice one, but it has to be done manually, so is problematic if one wants to play another instrument at the same time.
But it's useful if one just wants to listen.
Pasting the second pattern trailing the first one in a new double-length pattern, was the first I thought of too.
It has the advantage, that the second pattern doesn't necessary comes from the next pattern in the list.
So the option is more freely, compared to the 'From Position' function, which deals with a succeeding nr of N
This leads imo to a split of this request.
The most simple form is 'subsequent' patterns, whether 2 or more.
This could be achieved by an extra play-it-back button in the 'Wave Convert' dialog, if the 'From Position' is used.
Quite useful anyway to monitor the result, before rendering the WAV, because some 'Player' settings play a role there too.
Another form is dealing with non-subsequent patterns. So 2 or more patterns with different positions in the list.
'From-to' no longer valid. In this case, it would be nice to be able to select more than one pattern in the list :