check for undefined web3 coinbase

[danlipert]

Description

This PR checks to see if the coinbase check returns undefined, which isn't unexpected behavior (the encapsulating function is waiting for the web3 client to be ready) but is causing our alert system to go crazy lately.

Refers/Fixes

No issue

Testing

Tested creating a grant and funding it with a recurring donation manually.

[codecov]

Codecov Report

Merging #4250 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4250   +/-   ##
=======================================
  Coverage   30.24%   30.24%           
=======================================
  Files         209      209           
  Lines       16607    16607           
  Branches     2223     2223           
=======================================
  Hits         5022     5022           
  Misses      11404    11404           
  Partials      181      181

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[codecov]

Codecov Report

Merging #4250 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4250      +/-   ##
==========================================
+ Coverage   30.22%   30.24%   +0.01%     
==========================================
  Files         209      209              
  Lines       16619    16607      -12     
  Branches     2223     2223              
==========================================
- Hits         5023     5022       -1     
+ Misses      11415    11404      -11     
  Partials      181      181

Impacted Files	Coverage Δ
app/app/urls.py	90% <0%> (ø)	⬆️
app/dashboard/models.py	55.74% <0%> (ø)	⬆️
app/dashboard/views.py	13.77% <0%> (+0.05%)	⬆️

---

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