Merging r366451:

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r366451 | sureyeaah | 2019-07-18 17:38:03 +0200 (Thu, 18 Jul 2019) | 13 lines

[Clangd] Changed ExtractVariable to only work on non empty selections

Summary:
- For now, we don't trigger in any case if it's an empty selection
- Fixed unittests

Reviewers: kadircet, sammccall

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64912
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llvm-svn: 366714