[BugFix][C++] Fix next_chunk() of readers in the C++ library

[lixueclaire]

Proposed changes

When a vertex chunk has no edge, the next_chunk() function of readers for adj_list/adj_list_property may get errors since it reads a non-existing chunk.

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[github-actions]

🎊 PR Preview 726a92d has been successfully built and deployed to https://alibaba-graphar-build-pr-137.surge.sh

_{🤖 By surge-preview}

[acezen]

LGTM