Steps to reproduce the issue

1. Put a die statement at the end of method JArchivTar::extract in order to be able to inspect the contents of the extracted temporary files.
2. Install the .tar.gz version of this extension: https://github.com/JoomGallery/BootOne/releases/tag/v1.0-alpha5
3. Go to tmp/install_* and observe that the two files footer.bootone.php and header.bootone.php have been extracted into the root of this temporary directory instead of the folder BootOne-1.0-alpha5/administrator/components/com_joomgallery/layouts/joomgallery/common/ as in the original structure of the archive.

Expected result

Files footer.default.php and header.default.php should be extracted into tmp/install_*/BootOne-1.0-alpha5/administrator/components/com_joomgallery/layouts/joomgallery/common/.

Actual result

Files footer.default.php and header.default.php are extracted into tmp/install_*/.

System information (as much as possible)

Joomla! 3.5.1 on localhost with Xampp.

Additional comments