render bugs when isIdentity() is not consistent with getFramesNeeded()

[devernay]

Steps to Reproduce

1. reintroduce the bug fixed by https://github.com/NatronGitHub/openfx-misc/commit/ba5d100d6ae0e5baa62800c47c7a45cdd1443bbc
2. Create a graph CheckerBoard->Transform->FrameBlend
3. in Transform, add keyframes rotate=0@t=1, rotate=180@t=250
4. scrub the viewer timeline
5. in framerange, set min=-5 max=-5. This will trigger the isIdentity bug reintroduced in 1., and getFramesNeeded is now not consistent with isIdentity
6. Scrub the viewer timeline, there are rendering bugs

This should be fixed in Natron (Natron should be resilient to plugin bugs)

Also not that the interact position is the first frame in getFramesNeeded, not the frame given by isIdentity. If isIdentity returns true, the interact position should always be the one at the identity frame (thhe info given by getFramesNeeded is indicative only)

Versions

• Natron version/commit (they can be retrieved from the About Window): 2.3.10
• OS version:

[devernay]

This issue was moved to NatronGitHub/Natron#254