Fix non-0 terminated hostname str

wled00/wled.cpp

@@ -69,8 +69,9 @@ void prepareHostname(char* hostname)
   if (pos < 6) {
     sprintf(hostname + 5, "%*s", 6, escapedMac.c_str() + 6);
   } else { //last character must not be hyphen
+    hostname[pos] = '\0'; // terminate string
     while (pos > 0 && hostname[pos -1] == '-') {
-        hostname[pos -1] = 0;
+      hostname[pos -1] = '\0';
       pos--;
     }
   }