Fix Android SDCard path constant #174

Author: wkh237

src/android/src/main/java/com/RNFetchBlob/RNFetchBlobFS.java

@@ -197,7 +197,11 @@ static public Map<String, Object> getSystemfolders(ReactApplicationContext ctx)
         res.put("DownloadDir", Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).getAbsolutePath());
         res.put("MovieDir", Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MOVIES).getAbsolutePath());
         res.put("RingtoneDir", Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_RINGTONES).getAbsolutePath());
-//        res.put("SDCard", Environment.getExternalStorageDirectory().getAbsolutePath());
+        String state;
+        state = Environment.getExternalStorageState();
+        if (state.equals(Environment.MEDIA_MOUNTED)) {
+            res.put("SDCard", Environment.getExternalStorageDirectory().getAbsolutePath());
+        }
         res.put("MainBundleDir", ctx.getApplicationInfo().dataDir);
         return res;
     }