fix: handle unknown/undefined platform edge case (#5694)

Author: rigor789

lib/services/platform-environment-requirements.ts

@@ -152,9 +152,11 @@ export class PlatformEnvironmentRequirements
 			darwin: "macos",
 		} as any)[process.platform];
 
+		const anchor = platform ? `#${os}-${platform.toLowerCase()}` : ''
+
 		return (
 			`Verify that your environment is configured according to the system requirements described at\n` +
-			`https://docs.nativescript.org/environment-setup.html#${os}-${platform.toLowerCase()}.`
+			`https://docs.nativescript.org/environment-setup.html${anchor}.`
 		);
 	}