quick access - only switch to provider from help if it is not the default one

src/vs/platform/quickinput/browser/helpQuickAccess.ts

@@ -36,7 +36,7 @@ export class HelpQuickAccessProvider implements IQuickAccessProvider {
 		// name of a provider (e.g. `?term` for terminals)
 		disposables.add(picker.onDidChangeValue(value => {
 			const providerDescriptor = this.registry.getQuickAccessProvider(value.substr(HelpQuickAccessProvider.PREFIX.length));
-			if (providerDescriptor && providerDescriptor.prefix !== HelpQuickAccessProvider.PREFIX) {
+			if (providerDescriptor && providerDescriptor.prefix && providerDescriptor.prefix !== HelpQuickAccessProvider.PREFIX) {
 				this.quickInputService.quickAccess.show(providerDescriptor.prefix);
 			}
 		}));