Withdraw fixes

[rakanalh]

Based on @hackaugusto feedback in #4130

[codecov]

Codecov Report

Merging #4258 into develop will decrease coverage by 0.12%.
The diff coverage is 45.16%.

@@             Coverage Diff             @@
##           develop    #4258      +/-   ##
===========================================
- Coverage    81.15%   81.02%   -0.13%     
===========================================
  Files          103      103              
  Lines        13601    13631      +30     
  Branches      2074     2080       +6     
===========================================
+ Hits         11038    11045       +7     
- Misses        1962     1980      +18     
- Partials       601      606       +5

Impacted Files	Coverage Δ
raiden/network/proxies/payment_channel.py	92% <ø> (+5.33%)	⬆️
raiden/blockchain_events_handler.py	94.27% <100%> (ø)	⬆️
raiden/blockchain/events.py	94.39% <100%> (+0.1%)	⬆️
raiden/transfer/mediated_transfer/initiator.py	98.63% <100%> (ø)	⬆️
raiden/transfer/mediated_transfer/mediator.py	89.85% <100%> (+0.2%)	⬆️
raiden/network/proxies/token_network.py	56.55% <32.14%> (-0.67%)	⬇️
raiden/transfer/channel.py	88.98% <46.42%> (-1.66%)	⬇️
raiden/waiting.py	82.75% <0%> (-4.32%)	⬇️
raiden/raiden_service.py	88.26% <0%> (-0.24%)	⬇️
raiden/network/transport/matrix/transport.py	81.01% <0%> (-0.16%)	⬇️
... and 6 more

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