(mu_hdrent_find_stream_pos): Check for

hrd->tail != NULL.
(header_readline): Return immediately if header size is 0.

@@ -111,7 +111,7 @@ mu_hdrent_find_stream_pos (struct _mu_header *hdr, mu_off_t pos,
 	}
       x += strsize;
     }
-  if (x == pos)
+  if (x == pos && hdr->tail)
     {
       /* To supply the trailing '\n' */
       p = hdr->tail;
@@ -1048,7 +1048,12 @@ header_readline (mu_stream_t is, char *buffer, size_t buflen,
   status = mu_header_fill (header);
   if (status)
     return status;
-  
+  if (header->size == 0)
+    {
+      if (pnread)
+	*pnread = 0;
+      return 0;
+    }
   if (mu_hdrent_find_stream_pos (header, off, &ent, &ent_off))
     {
       if (pnread)