Add comments to explain why openAndTruncateStream()

app/src/main/java/org/schabi/newpipe/settings/export/ImportExportManager.kt

@@ -24,6 +24,8 @@ class ImportExportManager(private val fileLocator: BackupFileLocator) {
      */
     @Throws(Exception::class)
     fun exportDatabase(preferences: SharedPreferences, file: StoredFileHelper) {
+        // truncate the file before writing to it, otherwise if the new content is smaller than the
+        // previous file size, the file will retain part of the previous content and be corrupted
         ZipOutputStream(SharpOutputStream(file.openAndTruncateStream()).buffered()).use { outZip ->
             // add the database
             ZipHelper.addFileToZip(