Only commit log to disk if something was written in to it.

Without this, every write to the console results in log writes.

Only commit log to disk if something was written in to it.
843eecfc · Austin Clements · 7f1718ca · 843eecfc
--- a/log.c
+++ b/log.c
@@ -143,10 +143,12 @@ begin_trans(void)
 void
 commit_trans(void)
 {
+  if (log.lh.n > 0) {
    write_head();        // This causes all blocks till log.head to be commited
    install_trans();     // Install all the transactions till head
    log.lh.n = 0; 
    write_head();        // Reclaim log
+  }
  acquire(&log.lock);
  log.intrans = 0;