Support debugging without a workspace (#3728)

The existing code assumed there was always at least one workspace
folder, but this led to an error if there were zero. This can be
reproduced by calling "Close Workspace" if one is open and then running
Pester tests. Since the `vscode.debug.startDebugging()` interface does
not require a workspace folder, and in fact expects "undefined" if none
is available, we simply use TypeScript's "optional chaining" (AKA
conditional access) operator to return undefined if `workspaceFolders`
is null, and otherwise return the first workspace folder.

Author: andyleejordan

src/features/PesterTests.ts

@@ -144,6 +144,6 @@ export class PesterTestsFeature implements vscode.Disposable {
         // Ensure the necessary script exists (for testing). The debugger will
         // start regardless, but we also pass its success along.
         return utils.fileExists(this.invokePesterStubScriptPath)
-            && vscode.debug.startDebugging(vscode.workspace.workspaceFolders[0], launchConfig);
+            && vscode.debug.startDebugging(vscode.workspace.workspaceFolders?.[0], launchConfig);
     }
 }

src/features/RunCode.ts

@@ -49,7 +49,7 @@ export class RunCodeFeature implements vscode.Disposable {
             this.sessionManager.getSessionDetails());
 
         // TODO: Update to handle multiple root workspaces.
-        vscode.debug.startDebugging(vscode.workspace.workspaceFolders[0], launchConfig);
+        vscode.debug.startDebugging(vscode.workspace.workspaceFolders?.[0], launchConfig);
     }
 }