[DA] Fix function `removeMatchExtensions`

[sjoerdmeijer]

This is extracted from #160924 and little bit of a placeholder (more details will follow), but this is an attempt to document all know DA issues:

The complaint about function removeMatchExtensions was the following:

Removing zext can change the result (consider the value of zext(x) when x is a negative value)

I will add this to the meta issue #161805 that lists all DA issues.

[sjoerdmeijer]

CC: @kasuga-fj