Fix --new-window-if-not-first

The setting will now correctly open a new window when no file is specified, but if
a file is specified it will reuse. This is so opening via the file manager will reuse
the window.

Fixes #19775

src/vs/code/electron-main/launch.ts

@@ -94,7 +94,7 @@ export class LaunchService implements ILaunchService {
 		let usedWindows: VSCodeWindow[];
 		if (!!args.extensionDevelopmentPath) {
 			this.windowsService.openExtensionDevelopmentHostWindow({ context, cli: args, userEnv });
-		} else if (args._.length === 0 && args['new-window']) {
+		} else if (args._.length === 0 && (args['new-window'] || args['new-window-if-not-first'])) {
 			usedWindows = this.windowsService.open({ context, cli: args, userEnv, forceNewWindow: true, forceEmpty: true });
 		} else if (args._.length === 0) {
 			usedWindows = [this.windowsService.focusLastActive(args, context)];
@@ -103,7 +103,7 @@ export class LaunchService implements ILaunchService {
 				context,
 				cli: args,
 				userEnv,
-				forceNewWindow: args.wait || args['new-window'] || args['new-window-if-not-first'],
+				forceNewWindow: args.wait || args['new-window'],
 				preferNewWindow: !args['reuse-window'],
 				forceReuseWindow: args['reuse-window'],
 				diffMode: args.diff