Fix inconsistent default timecontrol.

As noted in pull request leela-zero#2172, the default
constructor set byo yomi stones but no time or
periods.

src/TimeControl.h

@@ -42,7 +42,7 @@ class TimeControl {
         Initialize time control. Timing info is per GTP and in centiseconds
     */
     TimeControl(int maintime = 60 * 60 * 100,
-                int byotime = 0, int byostones = 25,
+                int byotime = 0, int byostones = 0,
                 int byoperiods = 0);
 
     void start(int color);