Improve error handling

[bradjones1]

Fixes #306

[codecov]

Codecov Report

Patch coverage: 66.66% and project coverage change: -0.96 ⚠️

Comparison is base (0348af2) 99.27% compared to head (906985a) 98.32%.

❗ Current head 906985a differs from pull request most recent head 6e31baf. Consider uploading reports for the commit 6e31baf to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #307      +/-   ##
==========================================
- Coverage   99.27%   98.32%   -0.96%     
==========================================
  Files          11       11              
  Lines         416      418       +2     
  Branches       64       70       +6     
==========================================
- Hits          413      411       -2     
  Misses          3        3              
- Partials        0        4       +4     

Impacted Files	Coverage Δ
src/transports/EventEmitterTransport.ts	96.66% <66.66%> (-3.34%)	⬇️
src/transports/HTTPTransport.ts	97.72% <66.66%> (-2.28%)	⬇️
src/transports/TransportRequestManager.ts	97.84% <66.66%> (-1.06%)	⬇️
src/transports/WebSocketTransport.ts	97.14% <66.66%> (-2.86%)	⬇️

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[bradjones1]

Surprisingly, this doesn't break any tests! Probably means we need to add testing for this :-)

[bradjones1]

This is the key change. We may have an error response, which per the spec should result in an error response. The prior code block only checked to see if we were expecting the response with a particular ID, and early-returned. The processResult method would still reject the promise, however it would not return an error object.