upgrade: always use full text if "full-add" mode is enable

We should not be using a delta since the goal is to perform a full addition from
scratch in all cases.

Without this patch, `hg debugupgraderepo --optimize re-delta-fulladd --run` can
crash.

mercurial/revlog.py

@@ -2461,7 +2461,8 b' class revlog(object):'
                 # the revlog chunk is a delta.
                 cachedelta = None
                 rawtext = None
-                if destrevlog._lazydelta:
+                if (deltareuse != self.DELTAREUSEFULLADD
+                        and destrevlog._lazydelta):
                     dp = self.deltaparent(rev)
                     if dp != nullrev:
                         cachedelta = (dp, bytes(self._chunk(rev)))