[BUG] Match catch all statement

[simonegazza]

Description
Currently, there is no support for catch alla statement inside a match (i.e. _ guard inside a branch).

Expected behavior
This catch-all statement in match should be the entry of each statement if any other case in the match is descarded.

Suggested implementation
The problem needs further analysis but it is probably enough to simply rewrite the guard as a true statement evaluation.