ATRONIX: Decrease the Series_Memory when the series is freed

Or this stat doesn't make much sense. With this change, it now refers to
the series memory that's in use.

(cherry picked from commit 5057ccc)

Author: Oldes

src/core/m-pools.c

@@ -516,6 +516,7 @@ const REBPOOLSPEC Mem_Pool_Spec[MAX_POOLS] =
 	REBCNT n;
 
 	PG_Reb_Stats->Series_Freed++;
+	PG_Reb_Stats->Series_Memory -= SERIES_TOTAL(series);
 
 	// Remove series from expansion list, if found:
 	for (n = 1; n < MAX_EXPAND_LIST; n++) {