Avoid invalid session.loadPlugins early exit

`loadPlugins` sometimes get invoked before the project config is
available. In that case, it will not load the plugins, but when the
next chance comes to do so, it will take the early exit ("we already
tried to load plugins") instead of loading them.

Author: stefanv

packages/myst-cli/src/session/session.ts

@@ -164,9 +164,15 @@ export class Session implements ISession {
   async loadPlugins() {
     // Early return if a promise has already been initiated
     if (this._pluginPromise) return this._pluginPromise;
-    this._pluginPromise = loadPlugins(this);
-    this.plugins = await this._pluginPromise;
-    return this.plugins;
+
+    const state = this.store.getState();
+    const projConfig = selectors.selectCurrentProjectConfig(state);
+
+    if (projConfig) {
+      this._pluginPromise = loadPlugins(this);
+      this.plugins = await this._pluginPromise;
+      return this.plugins;
+    }
   }
 
   sourcePath(): string {