FileUpload total file size calculation

[martinoss]

I just noticed that the total file size calculation possibly has a bug.

It seems that when adding a single file, it will be counted twice for the total size over all files.

How to reproduce

1. Go to this storybook page: https://axa-ch-webhub-cloud.github.io/plib-feature/develop/?path=/story/components-file-upload--file-upload&args=maxSizeOfSingleFileKB:500;maxSizeOfAllFilesKB:999
   Notice that max single file size is capped at 500KB and max size of all files is 999KB
2. Add sample file (exactly 500KB) 500kb.pdf
3. Notice the error regarding the exceeded total file size for all files
4. Increase the limit from 999 to 1000, then it works.

A first look into the source suggests that these two lines probably needs to be flipped.

pattern-library/src/components/20-molecules/file-upload/index.js

Lines 442 to 443 in eca9f02

	this.sizeOfAllFilesInBytes += fileSize;
	this.validateOverallSize(fileSize);

On line 406, sizeOfAllFilesInBytes already has the value of 512000 when previewing the future total including the new file to be added.

pattern-library/src/components/20-molecules/file-upload/index.js

Lines 398 to 413 in eca9f02

	validateOverallSize(fileSize = 0) {
	const {
	sizeOfAllFilesInBytes,
	maxSizeOfAllFilesKB,
	filesTooBigStatusText,
	} = this;
	const maxSizeOfAllFilesInBytes = getBytesFromKilobyte(maxSizeOfAllFilesKB);
	if (sizeOfAllFilesInBytes + fileSize > maxSizeOfAllFilesInBytes) {
	this.globalErrorMessage = filesTooBigStatusText;
	this.invalid = true;
	} else {
	this.globalErrorMessage = '';
	this.invalid = false;
	}
	}