Disassembly selections now work even if no origin node is associated
with the disassembly code range that the user selects.

TBR=neis@chromium.org

Bug: v8:7327
Change-Id: Ib5bfcaded66deb65314fde7d3cb9ed2c3c4f6fe9
Notry: true
Reviewed-on: https://chromium-review.googlesource.com/c/1387492Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58423}