fix learner's wal is not empty in rare cases

[critical27]

What type of PR is this?

• bug
• feature
• enhancement

What problem(s) does this PR solve?

Issue(s) number:

Description:

See the comments in code, below is an example, previously if the part start as learner, all id is 0. But after 20220530-2344, things go wrong.

How do you solve it?

Clean wal is start as learner

Special notes for your reviewer, ex. impact of this fix, design document, etc:

Checklist:

Tests:

• Unit test(positive and negative cases)
• Function test
• Performance test
• N/A

Affects:

• Documentation affected (Please add the label if documentation needs to be modified.)
• Incompatibility (If it breaks the compatibility, please describe it and add the label.）
• If it's needed to cherry-pick (If cherry-pick to some branches is required, please label the destination version(s).)
• Performance impacted: Consumes more CPU/Memory

Release notes:

Please confirm whether to be reflected in release notes and how to describe:

ex. Fixed the bug .....

[codecov-commenter]

Codecov Report

Merging #4292 (ae0adf8) into master (fba3b18) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4292      +/-   ##
==========================================
+ Coverage   84.92%   84.94%   +0.01%     
==========================================
  Files        1328     1328              
  Lines      131930   131934       +4     
==========================================
+ Hits       112045   112072      +27     
+ Misses      19885    19862      -23     

Impacted Files	Coverage Δ
src/kvstore/raftex/RaftPart.cpp	70.14% <100.00%> (-1.83%)	⬇️
src/meta/processors/parts/GetSpaceProcessor.cpp	61.29% <0.00%> (-19.36%)	⬇️
src/common/thread/GenericWorker.h	80.76% <0.00%> (-3.85%)	⬇️
src/storage/mutate/AddEdgesProcessor.cpp	75.39% <0.00%> (-3.83%)	⬇️
src/codec/RowReaderWrapper.cpp	77.55% <0.00%> (-2.66%)	⬇️
src/common/base/Status.h	90.56% <0.00%> (-1.89%)	⬇️
src/storage/mutate/AddVerticesProcessor.cpp	86.32% <0.00%> (-1.71%)	⬇️
src/kvstore/Part.cpp	53.82% <0.00%> (-1.64%)	⬇️
src/common/meta/ServerBasedSchemaManager.cpp	84.37% <0.00%> (-1.05%)	⬇️
... and 27 more

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[critical27]

Don't merge now