title: TYPO3 won't accept images with the extension JPG
body: <p>I can upload files with the extension JPG and jpg to the filelist, but only files with extension jpg can be inserted in content elements. As soon as it is capital letters, I get an error.</p>
  
  <p>Is that a bug or where did I miss to check something?</p>
  
  <p>I use TYPO3 7.1.0</p>
  
  <p>The question is also asked here: <a href="https://forum.typo3.org/index.php/m/735666/#msg_735666" rel="nofollow">https://forum.typo3.org/index.php/m/735666/#msg_735666</a></p>