No need to remain paranoid when the actual root case is dead
simple (see previous commit)

This reverts commit f5ce5516.

Ref: #2645

As WS_Reset() clears the overflow marker, the correct order for
resetting and marking an overflow is WS_Reset(); WS_MarkOverflow();

Fixes the last seemingly obscure bit of #2645

If vbf_default_filter_list() returned without anything written to
the vsb (for no body or length 0), we would return as the filter
list whatever existed at ws->f + 1 prior to calling VBF_Get_Filter_List
(for example the string logged with std.log()).

Consequently, backend requests would fail with

	FetchError     Filter '...' not found

stuff there.

issue a membar to ensure that the overflow marker is written
before a failing WS allocation returns and is thus visible from
a different context.

pan_ic() already has an implicit membar via the mutex lock.

Ref #2645

list of VCLs" vs. "Do things with VCLs on list"

Ref: #2645

Spotted by:	slink

Should we plan to phase out synthetic() ?

Thank you to @martin-uplex for the review

Supress terminal responses by default and hope they look right.

Return HTC_S_OVERFLOW if exceeded.

This is a quick-fix for #2624, where we close the connection if a client
exceeds MAX_FRAME_SIZE. More proper handling with draining the rest of
the frame for the specific frames types that allow it (rfc7540 section
4.2) to come later.

Fixes: #2624

Fixes #2617