Fix/api

[seland]

Fixed several bugs in api:

• SendEthereumTransaction request was not closed correctly, caused it's always being closed by timeout.
• Panic caused by SendEthereumTransaction request cancellation (closing [api] panic while accessing an object on nil when signing an ethereum transaction #75).
• Invalid data passed to api using utf-8 encoded protobuf (closing [api] Unexpected EOF when successfully signed ethereum transaction #77).

[codecov-io]

Codecov Report

Merging #78 into develop will decrease coverage by 0.03%.
The diff coverage is 33.33%.

@@             Coverage Diff             @@
##           develop      #78      +/-   ##
===========================================
- Coverage    57.27%   57.24%   -0.04%     
===========================================
  Files           67       67              
  Lines         3696     3698       +2     
===========================================
  Hits          2117     2117              
- Misses        1136     1138       +2     
  Partials       443      443

Impacted Files	Coverage Δ
api/dapp.go	79.59% <33.33%> (-1.26%)	⬇️
dapp/request_limitation/throttling.go	32% <0%> (-4%)	⬇️
dapp/dapp.go	50% <0%> (-1.43%)	⬇️
dapp/registry/registry.go	42.6% <0%> (+1.73%)	⬆️

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[florianlenz]

Good work @seland