store: error out if fncache does not ends with a newline

If fncache does not ends with a newline, chunk will not be fully consumed. It
should be a bug somewhere or the fncache is corrupted if that happens. Let's
error out in such cases.

Differential Revision: https://phab.mercurial-scm.org/D6148

mercurial/store.py

@@ -481,6 +481,8 b' class fncache(object):'
                 # chunksize, so let's keep iterating
                 pass
 
+        if chunk:
+            raise error.Abort(_("fncache does not ends with a newline"))
         self._checkentries(fp)
         fp.close()