F_MALLOC: Fix "last free" line reports when debugging

If -DBG_MALLOC is in use, double free operations would report the
"first free" to actually be the malloc operation, which is incorrect.

mem/f_malloc.c

@@ -537,6 +537,12 @@ void fm_free(struct fm_block* qm, void* p)
 
 no_join:
 
+#ifdef DBG_MALLOC
+	f->file = file;
+	f->func = func;
+	f->line = line;
+#endif
+
 	fm_insert_free(qm, f);
 #if defined(DBG_MALLOC) || defined(STATISTICS)
 	qm->fragments -= 1;