Wraps file extension comparison components in strtolower()

[DanielGordonIT]

Created to fix #5095
This avoids the issue where replacing file.PNG with newfile.png fails due to "PNG" not being equal to "png"

[ssddanbrown]

Thanks @DanielGordonIT for providing this!

If you're confident with such a codebase, it would also be good to have a test to cover this scenario.
We have some test guidance here.
Here's an existing test related to this scenario, so an added test would be similar:

BookStack/tests/Uploads/ImageTest.php

Lines 122 to 139 in 14837e3

	public function test_image_file_update_does_not_allow_change_in_image_extension()
	{
	$page = $this->entities->page();
	$this->asEditor();
	$imgDetails = $this->files->uploadGalleryImageToPage($this, $page);
	$relPath = $imgDetails['path'];
	$newUpload = $this->files->uploadedImage('updated-image.jpg', 'compressed.png');
	$imageId = $imgDetails['response']->id;
	$this->call('PUT', "/images/{$imageId}/file", [], [], ['file' => $newUpload])
	->assertJson([
	"message" => "Image file replacements must be of the same type",
	"status" => "error",
	]);
	$this->files->deleteAtRelativePath($relPath);
	}

If you're not able to add this, that's fine, just let me know and I can write the test during review.

[DanielGordonIT]

I will work on creating a test for this tonight! If I am not able to make the test (PHP is not a language I am very familiar with, not that it's stopped me from using the theme system), I will let you know.

[DanielGordonIT]

@ssddanbrown I've added what I think would be a functional test case, but please do give it a review.

Wait no I did not the commit didn't work

[ssddanbrown]

This all looks good @DanielGordonIT, Thank you very much again for providing this and for putting in the extra effort to write a test! Merging for next patch release.