socket leak fix

* fix socket leak in "DownloadRunnable"
* in "DownloadInitializer" close the HTTP body after doing range-request checks
* in "DownloadRunnableFallback" fix typo in comment
* in "DownloadDialog" fix regression, using one thread for audios instead of subtitles

app/src/main/java/us/shandian/giga/get/DownloadRunnableFallback.java

@@ -94,7 +94,7 @@ public class DownloadRunnableFallback extends Thread {
                 mMission.notifyProgress(len);
             }
 
-            // if thread goes interrupted check if the last part mIs written. This avoid re-download the whole file
+            // if thread goes interrupted check if the last part is written. This avoid re-download the whole file
             done = len == -1;
         } catch (Exception e) {
             dispose();