Preserve growing countdown on groups with withered/grown plants

[sorten]

In a withered/grown group, still display the countdown if any plant is not withered/grown. This is useful if only some of your eight plants grew, but you still need to know how long until the rest die.

Specifically, this code:

1. Only updates the group timer if the incoming time is not min
2. Always prefers the incoming time if the group timer is min

[sorten]

Adds bug: headers do not inherit the updates to smallheader timers.