[clangd] Initialize int field to zero. NFC

To make sure we do not have uninitialized values and undefined behavior.

llvm-svn: 371081

clang-tools-extra/clangd/Protocol.h

@@ -1205,7 +1205,7 @@ llvm::json::Value toJSON(const FileStatus &FStatus);
 /// specific line of the text document.
 struct SemanticHighlightingInformation {
   /// The line these highlightings belong to.
-  int Line;
+  int Line = 0;
   /// The base64 encoded string of highlighting tokens.
   std::string Tokens;
 };