clang-format won't use .clang-format file on UNC-style network share out of box

Type: LanguageService

• OS and Version: Windows 10 1803
• VS Code Version: 1.23.1
• C/C++ Extension Version: 0.17.4
• The .clang-format file will not be used if the project resides on an UNC-style network share, unless the fallback style is forced to "none".
• This does not occur on drive-letter mounted network shares or local drives.

To Reproduce
Steps to reproduce the behavior:

1. Prepare a directory with a .clang-format file and some source on a network share like my \\10.0.1.15\zao\code\gggtools.
2. Open the folder with VS Code.
3. Open a C++ source file.
4. Hit the formatting shortcut.
5. Note that it doesn't use the .clang-format file, instead using the fallback style.
6. Configure "C_Cpp.clang_format_fallbackStyle": "none" in settings.
7. Format again.
8. Note how the .clang-format file is used as intended.

Expected behavior
I expect the formatter to always find and use the .clang-format file in the tree regardless of fallback style.

Reproduce the formatting failure using a .clang-format file on a UNC-style Windows network share, then compare it with a drive-letter share and a local drive. Trace the C/C++ extension's formatter and fallback-style handling; done means the tree's .clang-format file is used on UNC paths without requiring fallbackStyle to be set to "none".