Bazel client, Windows: fix AsShortWindowsPath

This method now works for non-existent paths too.

See https://github.com/bazelbuild/bazel/issues/2107

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PiperOrigin-RevId: 149284633
MOS_MIGRATED_REVID=149284633
diff --git a/src/main/cpp/util/file_platform.h b/src/main/cpp/util/file_platform.h
index 02f5b87..7733e7a 100644
--- a/src/main/cpp/util/file_platform.h
+++ b/src/main/cpp/util/file_platform.h
@@ -208,7 +208,9 @@
 bool AsWindowsPathWithUncPrefix(const std::string &path, std::wstring *wpath);
 
 // Same as `AsWindowsPath`, but returns a lowercase 8dot3 style shortened path.
-// Result will never have a UNC prefix.
+// Result will never have a UNC prefix, nor a trailing "/" or "\".
+// Works also for non-existent paths; shortens as much of them as it can.
+// Also works for non-existent drives.
 bool AsShortWindowsPath(const std::string &path, std::string *result);
 #endif  // defined(COMPILER_MSVC) || defined(__CYGWIN__)