Fix dbg_mean_of() to enable statistics when called

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/misc.cpp

@@ -96,6 +96,7 @@ void dbg_after() {
 void dbg_mean_of(int v) {
 
     assert(!dbg_show_hit_rate);
+    dbg_show_mean = true;
     dbg_cnt0++;
     dbg_cnt1 += v;
 }