improve tx cost computation

[bogdan-rosianu]

small improvement for the situation when the transaction to be estimated is a simple move balance

[codecov]

Codecov Report

Merging #3472 (83e74d3) into master (54b931d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3472   +/-   ##
=======================================
  Coverage   73.83%   73.84%           
=======================================
  Files         579      579           
  Lines       73420    73427    +7     
=======================================
+ Hits        54212    54219    +7     
- Misses      14837    14838    +1     
+ Partials     4371     4370    -1     

Impacted Files	Coverage Δ
process/transaction/transactionCostEstimator.go	74.01% <100.00%> (-2.66%)	⬇️
p2p/libp2p/netMessenger.go	75.00% <0.00%> (+0.41%)	⬆️
storage/txcache/txListBySenderMap.go	100.00% <0.00%> (+2.50%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 54b931d...83e74d3. Read the comment docs.

[gabi-vuls]

System test passed.
New error will be solved when development will go intro master.