To reproduce:
1. Open attached project and "animationWndskipKeyframe" scene
2. Open animation window (window->animation)
3. Select "animation10frames" in the project window
4. Move timeline using "go to next keyframe" and "go to previous keyframe"

Expected: No frames would be skipped when walking through them.
Actual: When moving from the 1st frame with "go to next keyframe" 5th frame is skipped, when moving from the last frame (10th) with "go to previous keyframe" 6th and 4th keyframes are skipped.

Reproduced with: 5.5.0f3, 5.6.2p2, 2017.1.0f2, 2017.2.0b2