Special handling for empty Json RPC Diagnostics (#125)

* Special handling for empty json diagnostics
See HaxeFoundation/haxe#11709

Author: kLabz

src/haxeLanguageServer/Context.hx

@@ -102,6 +102,12 @@ class Context {
 		final includeDisplayArguments = method.startsWith("display/") || method == ServerMethods.ReadClassPaths;
 		callDisplay(method, [Json.stringify(message)], token, function(result:DisplayResult) {
 			switch result {
+				case DResult("") if (method == DisplayMethods.Diagnostics):
+					haxeDisplayProtocol.handleMessage(({
+						jsonrpc: Protocol.PROTOCOL_VERSION,
+						id: (cast message : RequestMessage).id,
+						result: {result: []}
+					} : ResponseMessage));
 				case DResult(msg):
 					haxeDisplayProtocol.handleMessage(Json.parse(msg));
 				case DCancelled: