system mount: unmount system after checking for TWRP app

Change-Id: I9ab74c9839b50e399432d19839191b7de2d1bf60
(cherry picked from commit 07f991a3ed1457d4774078219e828e6d63756777)
diff --git a/twrp-functions.cpp b/twrp-functions.cpp
index 97387b7..593ad9d 100755
--- a/twrp-functions.cpp
+++ b/twrp-functions.cpp
@@ -1321,6 +1321,7 @@
 		}
 	}
 	DataManager::SetValue("tw_app_installed_in_system", 0);
+	PartitionManager.UnMount_By_Path(PartitionManager.Get_Android_Root_Path(), false);
 	return false;
 }