When keys are realized, strip handle positions are used to ensure, that
left and right key exists. If strip content is offset to the right,
this caused crash. This happened, because `SEQ_retiming_add_key()`
clamped timeline frame to strip content only on right side.
Clamp timeline frame to strip content on both sides.
Pull Request: https://projects.blender.org/blender/blender/pulls/124207
1f42c9eb54