Fix incorrect URL generation in getContentUrl()

[darth-antony]

trim($this->root, '/') strips the leading slash from the root path, making strlen() return a value 1 less than expected. This causes substr() to include an extra character from the root folder name in the relative path.

For example, with root folder "images":

• Expected URL: /files/image.jpg
• Actual URL: /files/s/image.jpg

Using strlen($this->root) + 1 is consistent with other URL construction methods in elFinderVolumeLocalFileSystem (lines 206, 612, 845, 1420) which all use this correct pattern.

Fixes #3746

[Smanst3r]

Any news on this https://github.com/Studio-42/elFinder/blob/master/php/elFinderVolumeDriver.class.php#L3334?
I have the same issue but I thought it could be done with rtrim($this->root..)... instead of trim($this->root...
and return rtrim($this->URL, '/') . $path;
Kind regards

[nao-pon]

@darth-antony That makes sense.

I think this became visible mainly in the immediate post-upload flow, where the backend has not yet exposed a stable stat URL and getContentUrl() is used directly. After reload, the normal stat data path hides the issue.

So the root cause explanation in the PR may be a bit simplified, but the fix direction itself still looks valid.