Handle missing plugins.

Fixes #24

react/src/PiPedalModel.tsx

@@ -1297,8 +1297,9 @@ class PiPedalModelImpl implements PiPedalModel {
 
         return nullCast(this.webSocket)
             .request<number>("saveCurrentPresetAs", request)
-            .then((data) => {
-                return data;
+            .then((newPresetId) => {
+                this.loadPreset(newPresetId);
+                return newPresetId;
             });
     }
     saveCurrentPluginPresetAs(pluginInstanceId: number, newName: string): Promise<number> {

react/src/PresetSelector.tsx

@@ -151,7 +151,7 @@ const PresetSelector =
                         return this.model.saveCurrentPresetAs(newName);
                     })
                     .then((newInstanceId) => {
-                        // s'fine. dealt with by updates, but we do need error handling.
+                        
                     })
                     .catch((error) => {
                         this.showError(error);