Fix revlog.parseindex

parseindex could fail if read returns too little data in the right
moment (e.g. when there's still leftover data from the previous
iteration and read returns less than "s" bytes).

mercurial/revlog.py

@@ -405,19 +405,17 b' class revlog(object):'
             if n == 0 and self.inlinedata():
                 # cache the first chunk
                 self.chunkcache = (0, data)
+            if leftover:
+                data = leftover + data
+                leftover = None
             off = 0
             l = len(data)
             while off < l:
                 if l - off < s:
                     leftover = data[off:]
                     break
-                if leftover:
-                    cur = leftover + data[off:off + s - len(leftover)]
-                    off += s - len(leftover)
-                    leftover = None
-                else:
-                    cur = data[off:off + s]
-                    off += s
+                cur = data[off:off + s]
+                off += s
                 e = struct.unpack(self.indexformat, cur)
                 self.index.append(e)
                 self.nodemap[e[-1]] = n