HTML filepicker multi - get files in use : <p>The following problem occured using Firefox v73 on Window 7:</p>

<p>In my code i use a multi-file-picker in html to upload up to 100-files parallal:</p>

<pre><code>&lt;input type="file" id="files" name="files" multiple&gt;
</code></pre>

<p>The files will be sent to a REST-API which process them afterwards.
When i select a single file (in the file-explorer) which is currently in use, i get a error-message (probably by window) which tells me, that the file cannot be picked because it is in use.
If i try to pick multiple-files which contain one or more files in use, i have no error occuring but the upload seems to stop when the file-in-use is reached and waiting for the file to be released.
This leads to request to wait for a timeout (which is 1 minute in my case).</p>

<p>Is there any option to catch the problem (in use file) before trying to upload the files?</p>

<p>PS: I've tried the same in Chrome and it returns a error before sending the request to the REST-API.</p>
