metrics: NilTimer should still run the function to be timed

[ucwong]

No description provided.

[codecov]

Codecov Report

Merging #1636 (b325ea8) into master (e0f2156) will increase coverage by 0.08%.
The diff coverage is 45.87%.

❗ Current head b325ea8 differs from pull request most recent head d51f27c. Consider uploading reports for the commit d51f27c to get more accurate results

@@            Coverage Diff             @@
##           master    #1636      +/-   ##
==========================================
+ Coverage   52.53%   52.62%   +0.08%     
==========================================
  Files         480      481       +1     
  Lines       59963    60210     +247     
==========================================
+ Hits        31501    31683     +182     
- Misses      26080    26117      +37     
- Partials     2382     2410      +28     

Impacted Files	Coverage Δ
cmd/utils/flags.go	1.84% <0.00%> (-0.01%)	⬇️
core/state/journal.go	72.54% <0.00%> (-2.97%)	⬇️
core/state/snapshot/conversion.go	0.00% <0.00%> (ø)
core/state/snapshot/generate.go	0.00% <0.00%> (ø)
core/state/snapshot/journal.go	0.00% <0.00%> (ø)
core/state/snapshot/snapshot.go	41.06% <0.00%> (-0.59%)	⬇️
core/types/state_account.go	0.00% <0.00%> (ø)
core/vm/gas_table.go	11.88% <ø> (+0.24%)	⬆️
core/vm/memory_table.go	0.00% <0.00%> (ø)
core/vm/opcodes.go	18.18% <ø> (ø)
... and 24 more

... and 9 files with indirect coverage changes