Restrict the amount to read when --stop-at-size is active so that reads, as well as writes, never go past --size bytes (#166).

src/include/pv-internal.h

@@ -395,6 +395,7 @@ struct pvstate_s {
 
 		size_t written_but_not_consumed; /* bytes in the output pipe, unread */
 
+		off_t total_bytes_read;		 /* total bytes read */
 		off_t total_written;		 /* total bytes or lines written */
 		off_t transferred;		 /* amount transferred (written - unconsumed) */