🐛 #1600 修复无法切换到初始公众号配置的问题并完善了removeConfigStorage方法

* 修复无法切换到初始公众号配置的问题

* 完善removeConfigStorage

weixin-java-mp/src/test/java/me/chanjar/weixin/mp/api/impl/BaseWxMpServiceImplTest.java

@@ -41,6 +41,7 @@ public class BaseWxMpServiceImplTest {
     assertTrue(this.wxService.switchover("another"));
     assertThat(WxMpConfigStorageHolder.get()).isEqualTo("another");
     assertFalse(this.wxService.switchover("whatever"));
+    assertFalse(this.wxService.switchover("default"));
   }
 
   @Test