fix unitialized local var

Local variables are not initialized by default. Make sure that buf[] is filled with zeros.

wled00/wled_server.cpp

@@ -507,7 +507,7 @@ String dmxProcessor(const String& var)
 
 void serveSettingsJS(AsyncWebServerRequest* request)
 {
-  char buf[SETTINGS_STACK_BUF_SIZE+37];
+  char buf[SETTINGS_STACK_BUF_SIZE+37] = { '\0' }; // WLEDMM ensure buffer is cleared initially
   buf[0] = 0;
   byte subPage = request->arg(F("p")).toInt();
   if (subPage > 10) {