Fix zip folder selection when storage path is similar

If internal is /sdcard and external is /sdcard-ext then the zip
path used to stay on /sdcard-ext when trying to switch to internal
storage. Using Get_Root_Path instead of resizing will ensure that
the path changes properly.
diff --git a/data.cpp b/data.cpp
index be76592..c766f00 100644
--- a/data.cpp
+++ b/data.cpp
@@ -556,8 +556,7 @@
 		if (zip_path.size() < storage_path.size()) {
 			SetValue(TW_ZIP_LOCATION_VAR, storage_path);
 		} else {
-			zip_root= zip_path;
-			zip_root.resize(storage_path.size());
+			zip_root = TWFunc::Get_Root_Path(zip_path);
 			if (zip_root != storage_path) {
 				LOGINFO("DataManager::SetBackupFolder zip path was %s changing to %s, %s\n", zip_path.c_str(), storage_path.c_str(), zip_root.c_str());
 				SetValue(TW_ZIP_LOCATION_VAR, storage_path);