Description of problem:
When playing around with architecture and going back and forth in wizard, liveusb-creator crashes with traceback:

Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/liveusb/gui.py", line 92, in run
    iso = self.grabber.urlgrab(self.progress.release.url, filename=filename, reget='simple')
  File "/usr/lib/python2.7/site-packages/urlgrabber/grabber.py", line 1172, in urlgrab
    return self._retry(opts, retryfunc, url, filename)
  File "/usr/lib/python2.7/site-packages/urlgrabber/grabber.py", line 1064, in _retry
    r = apply(func, (opts,) + args, {})
  File "/usr/lib/python2.7/site-packages/urlgrabber/grabber.py", line 1157, in retryfunc
    fo = PyCurlFileObject(url, filename, opts)
  File "/usr/lib/python2.7/site-packages/urlgrabber/grabber.py", line 1259, in __init__
    self._do_open()
  File "/usr/lib/python2.7/site-packages/urlgrabber/grabber.py", line 1598, in _do_open
    self._set_opts()
  File "/usr/lib/python2.7/site-packages/urlgrabber/grabber.py", line 1385, in _set_opts
    self.curl_obj.setopt(pycurl.NOPROGRESS, False)
pycurl.error: cannot invoke setopt() - perform() is currently running
Aborted



Version-Release number of selected component (if applicable):

liveusb-creator-3.92.1-1.fc24.noarch
python-pycurl-7.43.0-2.fc24.x86_64


Steps to Reproduce:
1. start liveusb-creator
2. select server
3. select 64bit
4. click 'Create Live USB'
5. click 'Cancel`
6. select 32bit
7. click 'Create Live USB'

Sometimes I needed to repeat steps 3-7.