revlog: avoid caching raw text too early in _revisiondata

Without this change, we could cache the rawtext without considering for it
validating the cache or not. If the exception raised by the invalid hash were to
be caught and the same revision accessed again, the invalid rawtext would be
returned.

mercurial/revlog.py

@@ -1633,11 +1633,14 b' class revlog(object):'
         rawtext = None
         # An intermediate text to apply deltas to
         basetext = None
+        # Do we need to update the rawtext cache once it is validated ?
+        needcaching = True
 
         # Check if we have the entry in cache
         # The cache entry looks like (node, rev, rawtext)
         if self._revisioncache:
             if self._revisioncache[0] == node:
+                needcaching = False
                 # _cache only stores rawtext
                 # rawtext is reusable. but we might need to run flag processors
                 rawtext = self._revisioncache[2]
@@ -1680,7 +1683,6 b' class revlog(object):'
 
             rawtext = mdiff.patches(basetext, bins)
             del basetext # let us have a chance to free memory early
-            self._revisioncache = (node, rev, rawtext)
 
         if flags is None:
             if rev is None:
@@ -1691,6 +1693,9 b' class revlog(object):'
         if validatehash:
             self.checkhash(text, node, rev=rev)
 
+        if needcaching:
+            self._revisioncache = (node, rev, rawtext)
+
         return text
 
     def rawdata(self, nodeorrev, _df=None):