Fixed dbg scripts to allow explicit trunks without checksums

Note this is intentionally different from how lfsr_rbyd_fetch behaves
in lfs.c. We only call lfsr_rbyd_fetch when we need validated checksums,
otherwise we just don't fetch.

The dbg scripts, on the other hand, always go through fetch, but it is
useful to be able to inspect the state of incomplete trunks when
debugging.

This use to be how the dbg scripts behaved, but they broke because of
some recent script work.

scripts/dbgrbyd.py

@@ -981,6 +981,10 @@ def main(disk, blocks=None, *,
                         # keep track of eoff for best matching trunk
                         if trunk and j_ + size > trunk:
                             trunkeoff = j_ + size
+                            eoff = trunkeoff
+                            cksum = cksum_
+                            trunk_ = trunk__
+                            weight = weight_
 
             if not tag & TAG_ALT:
                 j_ += size