And fix the h2_req VDP error handling as per the VDP contract.

Test case inspired by Simon. Since this is one of those test cases that
explicitly mix two features I wasn't sure whether I wanted to make this
an h2 test case or a range test case. Since this was ultimately a range
bug I decided to register it in a range test case.

It's not obvious what should have been authoritative here. The range VDP
was rightfully latching an error via SC_RANGE_SHORT that is defined as an
error-type session close reason, but VDP_DeliverObj() doesn't take that
into account. While SC_RANGE_SHORT isn't a session/protocol error for h2
but rather a stream error it is not obvious what VDP_DeliverObj() should
do in the absence of a negative retval and the presence of a non-null
sess_close.

Maybe another way could be to turn enum sess_close into a struct and
embed http1 and h2 specificities directly in struct fields. We already
have somewhat structured information in the sess_close.h table.

Refs 03f71c6e