Fix bug that prevented just the coordinator from permitting joins

[puddly]

fbaa528 introduced a bug where joins could not be permitted on the coordinator alone anymore.

[codecov-commenter]

Codecov Report

Merging #86 (08793ae) into dev (b1ded73) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##              dev      #86      +/-   ##
==========================================
- Coverage   98.71%   98.68%   -0.03%     
==========================================
  Files          44       44              
  Lines        3725     3727       +2     
==========================================
+ Hits         3677     3678       +1     
- Misses         48       49       +1     

Impacted Files	Coverage Δ
zigpy_znp/zigbee/application.py	95.74% <100.00%> (-0.16%)	⬇️

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