fix: pending property for PaymentStatus

[motorina0]

A payment status is pending when the paid value is none.

In the old implementation if a payment was failed (paid == False) then the pending property would be True (which is incorrect)

[codecov]

Codecov Report

Attention: Patch coverage is 30.76923% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 57.83%. Comparing base (352fd23) to head (2287503).

Files	Patch %	Lines
lnbits/wallets/lnbits.py	0.00%	7 Missing ⚠️
lnbits/wallets/fake.py	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #2324      +/-   ##
==========================================
- Coverage   58.56%   57.83%   -0.74%     
==========================================
  Files          61       61              
  Lines        9210     9218       +8     
==========================================
- Hits         5394     5331      -63     
- Misses       3816     3887      +71     

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[motorina0]

fixing failed jobs...