compute the hash of the proposal iff the proposal hash is present

[Stebalien]

Previously, we'd always compute the hash but only compare it if it was specified. This simply increased the cost of messages that didn't specify the hash for no good reason.

fixes #1364

[Stebalien]

@anorth please check this thoroughly. I believe this is the correct thing to do, but I'm not familiar with why the code was written the way it was in the first place.

[codecov-io]

Codecov Report

Merging #1365 (0167588) into master (c7ea991) will not change coverage.
The diff coverage is 100.0%.

@@          Coverage Diff           @@
##           master   #1365   +/-   ##
======================================
  Coverage    69.5%   69.5%           
======================================
  Files          72      72           
  Lines        7638    7638           
======================================
  Hits         5310    5310           
  Misses       1437    1437           
  Partials      891     891           

[ZenGround0]

Looks good. Adding tests before merging.

[codecov-commenter]

Codecov Report

Merging #1365 (973af29) into master (3c34498) will not change coverage.
The diff coverage is 100.0%.

@@          Coverage Diff           @@
##           master   #1365   +/-   ##
======================================
  Coverage    71.1%   71.1%           
======================================
  Files          72      72           
  Lines        8395    8395           
======================================
  Hits         5975    5975           
  Misses       1574    1574           
  Partials      846     846           

[ZenGround0]

@droark do you see any problems with this?

[droark]

👍

I'd prefer that the PR not be pulled for another day, in case I think of some reason why this shouldn't be pulled, but I'm pretty sure this is safe. I can't think of any reasons why a hash should be mandatory in this situation. The modified logic seems safe too.