fix bug

hutool-http/src/main/java/org/dromara/hutool/http/client/engine/httpclient4/HttpClient4Engine.java

@@ -63,6 +63,7 @@ public class HttpClient4Engine implements ClientEngine {
 	 * 构造
 	 */
 	public HttpClient4Engine() {
+		initEngine();
 	}
 
 	@Override

hutool-http/src/main/java/org/dromara/hutool/http/client/engine/httpclient5/HttpClient5Engine.java

@@ -67,6 +67,7 @@ public class HttpClient5Engine implements ClientEngine {
 	 * 构造
 	 */
 	public HttpClient5Engine() {
+		initEngine();
 	}
 
 	@Override

hutool-http/src/main/java/org/dromara/hutool/http/client/engine/okhttp/OkHttpEngine.java

@@ -43,7 +43,9 @@ public class OkHttpEngine implements ClientEngine {
 	/**
 	 * 构造
 	 */
-	public OkHttpEngine() {}
+	public OkHttpEngine() {
+		initEngine();
+	}
 
 	@Override
 	public OkHttpEngine init(final ClientConfig config) {