【BUG】修复用户上报bug：在dismiss之前需要做isShowing的判断。crash log如下：
java.lang.IllegalArgumentException: View=com.android.internal.policy.impl.PhoneWindow$DecorView{42147e30 V.E..... R.....I. 0,0-700,345} not attached to window manager
at android.view.WindowManagerGlobal.findViewLocked(WindowManagerGlobal.java:370)
at android.view.WindowManagerGlobal.removeView(WindowManagerGlobal.java:299)
at android.view.WindowManagerImpl.removeViewImmediate(WindowManagerImpl.java:109)
at android.app.Dialog.dismissDialog(Dialog.java:338)
at android.app.Dialog.dismiss(Dialog.java:321)