Description of problem:
rpmlint is backtracing for me when run on an rpm.

Version-Release number of selected component (if applicable):
rpmlint-1.9-8.fc25

How reproducible:
100%

Steps to Reproduce:
1. rpmlint <name-version-release.arch.rpm>

Actual results:
0 packages and 0 specfiles checked; 0 errors, 0 warnings.
Traceback (most recent call last):
  File "/usr/bin/rpmlint", line 371, in <module>
    main()
  File "/usr/bin/rpmlint", line 160, in main
    runChecks(pkg)
  File "/usr/bin/rpmlint", line 217, in runChecks
    check.check(pkg)
  File "/usr/share/rpmlint/AbstractCheck.py", line 50, in check
    return self.check_binary(pkg)
  File "/usr/share/rpmlint/DistributionCheck.py", line 40, in check_binary
    for fname in pkg.files():
  File "/usr/share/rpmlint/Pkg.py", line 611, in files
    self._gatherFilesInfo()
  File "/usr/share/rpmlint/Pkg.py", line 721, in _gatherFilesInfo
    pkgfile.magic = b2s(_magic.descriptor(fd))
  File "/usr/share/rpmlint/Pkg.py", line 48, in b2s
    return b.decode(errors='replace')
AttributeError: 'str' object has no attribute 'decode'

Expected results:
no error