Fixed bug in tc.log recovery code that caused crash_commit_before to sometimes crash.

sql/log.cc

@@ -5154,8 +5154,8 @@ int TC_LOG_MMAP::open(const char *opt_name)
     pthread_mutex_init(&pg->lock, MY_MUTEX_INIT_FAST);
     pthread_cond_init (&pg->cond, 0);
     pg->start=(my_xid *)(data + i*tc_log_page_size);
-    pg->end=(my_xid *)(pg->start + tc_log_page_size);
     pg->size=pg->free=tc_log_page_size/sizeof(my_xid);
+    pg->end=pg->start + pg->size;
   }
   pages[0].size=pages[0].free=
                 (tc_log_page_size-TC_LOG_HEADER_SIZE)/sizeof(my_xid);