Fixes transitioning API delay when delayMs is not set

[tomasgcs]

After implamenting "Slow Transitions" feature an issue was introduced with Transitioning API as you can see here tomasgcs@4ef8b81#diff-a7ea5763fc80cde0b741dca6a5095a18R46

Previously beginTime variable was not set at all which was equal to 0, but after this specific line was added the value is different, and it causes animations to delay even if delayMs value is not set, this happens only when animation is is being executed multiple times.

Not sure why this is happening but most likely that CACurrentMediaTime() introduces delay even if it takes current time. In my case it is very important to run animations as fast as possible so I've sumbitted a fix here.

[tomasgcs]

@kmagiera Hello, could you take a look at this PR?

[kmagiera]

I'm fine with merging this change in. However, I'd like to have a comment here explaining why this check has been introduced (basically what you explain in the PR description).

I also wonder what is the delay in case we use CACurrentMediaTime(). Is this like 1 frame delay (16ms) or more than that? Also if you set delay to be 60 ms is it going to start after 60ms or after 60ms + 1 frame

[osdnk]

ping @tomasgcs

[tomasgcs]

Apologies for delays, added a comment for the check. Also found an article about CACurrentMediaTime:
https://bendodson.com/weblog/2013/01/29/ca-current-media-time/

as Apple in apple docs

A CFTimeInterval derived by calling mach_absolute_time() and converting the result to seconds.

So I am thinking that it might be rounding issue or something like that.

[tomasgcs]

@osdnk @kmagiera

Check my latest commit an new issue was introduced with this commit

50e695f#diff-7ab6d44707ac6cd944a490906c842dbb

backwards compatable animations stopped working.

[osdnk]

Looks good! Please ping whenever you'll find it mergeable

[tomasgcs]

@osdnk

Animations are fixed here:
4d98f4f

And I already added comments for _delay animations issue here:
24401b4

Apologies for not creating a separate PR for backward compatible animations fix. But I can do that if necessary.