zink: fix broken pool-alloc consolidation

zink: fix broken pool-alloc consolidation

When appending the content of a util_dynarray to another util_dynarray, we
need to copy the content to the *end* of the util_dynarray, not the
beginning.

As we've already resized the dynarray, We also shouldn't add to the size
once more at the end, otherwise we'll end up with garbage.

Fixes: 43dcdf33654 ("zink: rework/improve descriptor pool overflow handling on batch reset")
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/7485
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19068>