Current inpipe remains unchaged in XREP when other pipe terminates

When an inpipe terminated within XREP, it was erased from the array
and thus current_in (which is an index) pointed to a different
element in the array. This caused problems when we were in the
middle of reading a multipart message.
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/xrep.cpp

@@ -101,10 +101,10 @@ void zmq::xrep_t::terminated (reader_t *pipe_)
           ++it) {
         if (it->reader == pipe_) {
             inpipes.erase (it);
+            if ((inpipes_t::size_type) (it - inpipes.begin ()) < current_in)
+                current_in--;
             if (terminating)
                 unregister_term_ack ();
-            if (current_in >= inpipes.size ())
-                current_in = 0;
             return;
         }
     }