Blender Git Loki

Fix T85426: Speed effect stretch to input not working

`seq_effect_speed_get_strip_content_length()` checked only for number
of inputs of target strip, even if it's not an effect.

Only effects are treated in different way, so check for type as well.
Broken by 93c10797dc35e17bbd96f3711a151acf2d184848

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D10356