fix infinite loop in `stats bw`

"break" just breaks from the select, this loops infinitely (fast).

License: MIT
Signed-off-by: Steven Allen <steven@stebalien.com>

core/commands/stat.go

@@ -142,7 +142,7 @@ Example:
 			select {
 			case <-time.After(interval):
 			case <-req.Context.Done():
-				break
+				return nil
 			}
 		}
 	},