Super long saving time in backend

Hi,

we do have the problem that any saving action in the backend takes about 30 seconds. We also find the error, mayby you can fix it in a future release? Problem is function prepareSlideData in admin/assets/dist/js/app.min.js

In prepareSlideData you do

###
prepareSlideData(data) {
	let slides = data.filter(input => input.name.startsWith('attachment'))
	let allSlides = []
	let currentSlide = ''
	slides.forEach(slide => {

		// Grab the id from a string like "attachment[2069][]"
		let thisSlide = slide.name.match(/attachment\[([\s\S]*?)\]/)[1]
		currentSlide = (currentSlide != thisSlide) ? thisSlide : currentSlide
		if ('undefined' === typeof allSlides[currentSlide]) {
			allSlides[currentSlide] = []
		}
		allSlides[currentSlide].push(slide)
	})
},
return allSlides.filter(val => val) // re-index
###

We do have very high post ids (987484571 for example). 

This means that before

allSlides.filter(val => val)

the allSlides is an array with for example three items

allSlides[987484571] = array
allSlides[987484572] = array
allSlides[987484573] = array

When you use allSlides.filter it takes about 30 Seconds because of starting at index 1 an iterating ...

I fixed it by do something like that

prepareSlideData(data) {
	let slides = data.filter(input => input.name.startsWith('attachment'))
	let allSlides = []
	let allSlidesIndex = []
	let allSlidesFinal = []
	let currentSlide = ''
	slides.forEach(slide => {

		// Grab the id from a string like "attachment[2069][]"
		let thisSlide = slide.name.match(/attachment\[([\s\S]*?)\]/)[1]
		currentSlide = (currentSlide != thisSlide) ? thisSlide : currentSlide
		if ('undefined' === typeof allSlides[currentSlide]) {
			allSlides[currentSlide] = []
			allSlidesIndex.push(currentSlide)
		}
		allSlides[currentSlide].push(slide)
	})
	allSlidesIndex.forEach(index => {
		allSlidesFinal.push(allSlides[index])
	})
	return allSlidesIndex
},

can you test and implemnt this?