revlog: deal with chunk ranges over 2G on Windows (issue4215)

Python uses a C long (32 bits on Windows 64) rather than an ssize_t in
read(), and thus has a 2G size limit. Work around this by falling back
to reading one chunk at a time on overflow. This approximately doubles
our headroom until we run back into the size limit on single reads.

mercurial/revlog.py

@@ -909,8 +909,13 b' class revlog(object):'
         ladd = l.append
 
         # preload the cache
+        try:
         self._chunkraw(revs[0], revs[-1])
         offset, data = self._chunkcache
+        except OverflowError:
+            # issue4215 - we can't cache a run of chunks greater than
+            # 2G on Windows
+            return [self._chunk(rev) for rev in revs]
 
         for rev in revs:
             chunkstart = start(rev)