Fixed regression of loader spindle during extension installation

[beat]

This regression got introduced with commit 87db28b in PR #7235

Instructions for testers:

1. Checkout master or Joomla 3.5 beta 2, try installing an extension through upload or by web: See that there is no Joomla spindle during upload and install.
2. Try this branch and do same: See that there is a Joomla spindle like was the case in Joomla 3.4.3 and before.

[brianteeman]

I have tested this item ✅ successfully on 8644bd3

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[cyrezdev]

I have tested this item ✅ successfully on 8644bd3

Tested successfully on 3.5.0-beta2, and works like it was the case in Joomla 3.4.8 and before.
Thanks!

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[beat]

Thanks to testers and to the maintainer for fast action 😄