reduce conversion of argument 'query-item' of fetch/config command into string

Author: smdn

src/Smdn.Net.MuninNode/Smdn.Net.MuninNode/NodeBase.Protocol.cs

@@ -250,8 +250,9 @@ CancellationToken cancellationToken
   {
     ThrowIfPluginProviderIsNull();
 
+    var queryItem = Encoding.GetString(arguments);
     var plugin = PluginProvider.Plugins.FirstOrDefault(
-      plugin => string.Equals(Encoding.GetString(arguments), plugin.Name, StringComparison.Ordinal)
+      plugin => string.Equals(queryItem, plugin.Name, StringComparison.Ordinal)
     );
 
     if (plugin is null) {
@@ -308,8 +309,9 @@ CancellationToken cancellationToken
   {
     ThrowIfPluginProviderIsNull();
 
+    var queryItem = Encoding.GetString(arguments);
     var plugin = PluginProvider.Plugins.FirstOrDefault(
-      plugin => string.Equals(Encoding.GetString(arguments), plugin.Name, StringComparison.Ordinal)
+      plugin => string.Equals(queryItem, plugin.Name, StringComparison.Ordinal)
     );
 
     if (plugin is null) {