fix(anim_timeline) avoid calling lv_anim_del(NULL, NULL)

[FASTSHIFT]

Description of the feature or fix

This PR is about the resolution of #2589.
Avoid calling lv_anim_del(NULL, NULL) to cause all animations to be deleted.

Checkpoints

• Follow the styling guide
• Update CHANGELOG.md
• Update the documentation

[kisvegabor]

So far I thought that an animation doesn't make much sens if neither var nor exec_cb is set. But setting only the ready_cb might be also valid use case, especially in case of anim timeline.

An other solution could be to add a dummy callback to exec_cb in lv_anim_timeline_add if it's NULL.

BTW, won't the current solution (in this PR) cause memory leak?

[FASTSHIFT]

So far I thought that an animation doesn't make much sens if neither nor is set. But setting only the might be also valid use case, especially in case of anim timeline.var``exec_cb``ready_cb

An other solution could be to add a dummy callback to in if it's .exec_cb``lv_anim_timeline_add``NULL

BTW, won't the current solution (in this PR) cause memory leak?

Why is there a memory leak, is it lv_anim_timeline or lv_anim?

[kisvegabor]

Why is there a memory leak, is it lv_anim_timeline or lv_anim?

Because if both var and exec_cb are NULL the animation won't be deleted.

[FASTSHIFT]

Why is there a memory leak, is it lv_anim_timeline or lv_anim?

Because if both var and exec_cb are NULL the animation won't be deleted.

lv_anim will automatically delete the animation when the animation reaches the set end time. No need to actively call lv_anim_del to delete.

[kisvegabor]

But if an animation is not deleted in lv_anim_timeline_stop it will keep running and it will call its ready_cb. However, the user intention was to make all animations stop.

[FASTSHIFT]

You are right. I thought of a solution: When it is detected that var and exec_cb are NULL, use the pointer of lv_anim_timeline as var, so that the animation can be completely deleted when lv_anim_timeline_stop is called.

[kisvegabor]

Looks good, thank you!