[Cin] BUG on Clear keyframes (CinGG-release by GIT 30Aug 2020)

[Andrea paz]

Try the latest release. Sometimes it works well, other times it still
gives the interval problems of yesterday. In case of errors, if you
make an undo and repeat the interval changes, the second time it works
fine!
Instead, the problem of subsequent edits that varied even if not
affected by the keyframes range is solved: now they remain intact.