rev-branch-cache: fix message about overwritten data

If there is data at the end we ignore, we should not count them as overwritten.

This reveal that we something don't overwrite anything, this will be taken car
of in the next changeset.

mercurial/branching/rev_cache.py

@@ -399,8 +399,9 class revbranchcache:
                 threshold = current_size * REWRITE_RATIO
                 if (max(end, current_size) - start) < threshold:
                     # end affected, let overwrite the bad value
+                    overwritten = min(end, current_size) - start
                     dbg = b"overwriting %d bytes from %d in cache/%s"
-                    dbg %= (current_size - start, start, _rbcrevs)
+                    dbg %= (overwritten, start, _rbcrevs)
                     if end < current_size:
                         extra = b" leaving (%d trailing bytes)"
                         extra %= current_size - end

tests/test-branches.t

@@ -835,7 +835,7 recovery from invalid cache revs file wi
   $ echo >> .hg/cache/rbc-revs-v2
   $ rm -f .hg/cache/branch* && hg head a -T '{rev}\n' --debug
   5
-  overwriting 2 bytes from 160 in cache/rbc-revs-v2 leaving (2 trailing bytes)
+  overwriting 0 bytes from 160 in cache/rbc-revs-v2 leaving (2 trailing bytes)
   $ f --size .hg/cache/rbc-revs*
   .hg/cache/rbc-revs-v2: size=162