Trivial: Refactor `if` statement for the pending block

[linked0]

It's just for making the code more readable.

[codecov[bot]]

Codecov Report

Merging #3257 (bb746c6) into v0.x.x (9c56ea5) will increase coverage by 35.01%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           v0.x.x    #3257       +/-   ##
===========================================
+ Coverage   53.54%   88.55%   +35.01%     
===========================================
  Files         332      166      -166     
  Lines       35818    17034    -18784     
===========================================
- Hits        19178    15085     -4093     
+ Misses      16640     1949    -14691     

Flag	Coverage Δ
integration	42.27% <ø> (+18.52%)	:arrow_up:
unittests	87.65% <100.00%> (+0.05%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
source/agora/consensus/protocol/Nominator.d	91.99% <100.00%> (+1.11%)	:arrow_up:
source/agora/common/VibeTask.d	0.00% <0.00%> (-80.00%)	:arrow_down:
source/agora/common/FileBasedLock.d	0.00% <0.00%> (-72.73%)	:arrow_down:
source/scpd/scp/SCPDriver.d	60.00% <0.00%> (-15.00%)	:arrow_down:
source/agora/consensus/BlockStorage.d	68.90% <0.00%> (-11.31%)	:arrow_down:
source/agora/node/Runner.d	40.52% <0.00%> (-9.81%)	:arrow_down:
source/agora/node/Config.d	71.90% <0.00%> (-9.10%)	:arrow_down:
source/agora/node/Registry.d	77.61% <0.00%> (-2.35%)	:arrow_down:
source/agora/network/Client.d	87.12% <0.00%> (-2.28%)	:arrow_down:
source/agora/common/DNS.d	87.96% <0.00%> (-0.40%)	:arrow_down:
... and 172 more

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[linked0]

Merging as it is all green.