validate the address when APIService.GetAccount() is called.

[DevYohanPark]

According to secp256k1 spec, compressed public key should start with "02" or "03".

[codecov-io]

Codecov Report

Merging #13 into master will increase coverage by 0.36%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #13      +/-   ##
==========================================
+ Coverage   64.36%   64.73%   +0.36%     
==========================================
  Files          86       89       +3     
  Lines        9901    10268     +367     
==========================================
+ Hits         6373     6647     +274     
- Misses       2646     2760     +114     
+ Partials      882      861      -21

Impacted Files	Coverage Δ
rpc/api_service.go	76.33% <100%> (+5.75%)	⬆️
net/utils.go	51.11% <0%> (-33.51%)	⬇️
common/types.go	62.22% <0%> (-15.56%)	⬇️
net/peer_filters.go	56.25% <0%> (-12.5%)	⬇️
util/hex/hex.go	80.35% <0%> (-12.43%)	⬇️
common/trie/iterator.go	74.61% <0%> (-11.23%)	⬇️
rpc/gateway.go	43.75% <0%> (-9.59%)	⬇️
util/logging/loggers.go	79.71% <0%> (-9.48%)	⬇️
rpc/mapper.go	83.8% <0%> (-7.4%)	⬇️
consensus/dpos/dpos_transaction.go	48.84% <0%> (-6.65%)	⬇️
... and 60 more

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