Unused assignment in Nebula Code

[FloridSleeves]

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Describe the bug (required)
There are some unused assignment in Nebula code, which may indicate bugs. Some are unlogged exceptions, some are unchecked return value.

Your Environments (required)

• OS: Linux 5.11.0-40-generic Ubuntu 20.04.2
• Compiler: clang version 10.0.0-4ubuntu1
• CPU: Intel(R) Core(TM) i5-9500 CPU @ 3.00GHz

How To Reproduce(required)

There are some unused assignment in Nebula code, which may indicate bugs:

File	Line	Variable	Explanation
src/kvstore/NebulaStore.cpp	161	e	Exception may need to be also logged by e.what()
src/storage/query/ScanEdgeProcessor.cpp	66	ret	return value of handleEdgeProps() need check whether is nebula::cpp2::ErrorCode::SUCCEEDED
src/storage/query/ScanVertexProcessor.cpp	69	ret	return value of handleVertexProps() need check whether is nebula::cpp2::ErrorCode::SUCCEEDED
src/codec/RowReaderV1.cpp	454	ex	Exception may need to be also logged by ex.what()
src/kvstore/wal/FileBasedWal.cpp	100	ex	Exception may need to be also logged by ex.what()
src/codec/RowReaderV1.cpp	454	ex	Exception may need to be also logged by ex.what()

The unchecked return value may cause wrong assumption on completeness of previous task and result in data corruption. And the unlogged exception may impede diagnosis of program failure.

Could you please help to confirm whether they are bugs?

Expected behavior

The assigned value is used or checked.

Additional context

[FloridSleeves]

Hi! Thanks for adding them to v3.1.0 milestone! Can I make a pull request to fix them?