Caller.java : Fix NullPointerException in createResultFromInputStream

    * This is the error - E/AndroidRuntime(10584): FATAL EXCEPTION: AsyncTask #1
E/AndroidRuntime(10584): java.lang.RuntimeException: An error occured while executing doInBackground()
E/AndroidRuntime(10584): 	at android.os.AsyncTask$3.done(AsyncTask.java:299)
E/AndroidRuntime(10584): 	at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
E/AndroidRuntime(10584): 	at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
E/AndroidRuntime(10584): 	at java.util.concurrent.FutureTask.run(FutureTask.java:239)
E/AndroidRuntime(10584): 	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
E/AndroidRuntime(10584): 	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
E/AndroidRuntime(10584): 	at java.lang.Thread.run(Thread.java:841)
E/AndroidRuntime(10584): Caused by: java.lang.NullPointerException: lock == null
E/AndroidRuntime(10584): 	at java.io.Reader.<init>(Reader.java:64)
E/AndroidRuntime(10584): 	at java.io.InputStreamReader.<init>(InputStreamReader.java:79)
E/AndroidRuntime(10584): 	at com.andrew.apollo.lastfm.Caller.createResultFromInputStream(Caller.java:216)
E/AndroidRuntime(10584): 	at com.andrew.apollo.lastfm.Caller.call(Caller.java:143)
E/AndroidRuntime(10584): 	at com.andrew.apollo.lastfm.Artist.getInfo(Artist.java:73)
E/AndroidRuntime(10584): 	at com.andrew.apollo.lastfm.Artist.getInfo(Artist.java:55)
E/AndroidRuntime(10584): 	at com.andrew.apollo.cache.ImageFetcher.processImageUrl(ImageFetcher.java:117)
E/AndroidRuntime(10584): 	at com.andrew.apollo.cache.ImageWorker$BitmapWorkerTask.doInBackground(ImageWorker.java:238)
E/AndroidRuntime(10584): 	at com.andrew.apollo.cache.ImageWorker$BitmapWorkerTask.doInBackground(ImageWorker.java:155)
E/AndroidRuntime(10584): 	at android.os.AsyncTask$2.call(AsyncTask.java:287)
E/AndroidRuntime(10584): 	at java.util.concurrent.FutureTask.run(FutureTask.java:234)
E/AndroidRuntime(10584): 	... 3 more

    * Steps to reproduce - Simply connect to a wifi network which doesn't work
    (like a phone's portable wifi hotspot which doesn't have a data connection)
    and open Apollo. It will fc within 10 seconds. This bug would also cause Apollo to simply crash without a stack trace, if opened for the first time under the above conditions.

Change-Id: Id6582005bf0f20df815c65714a2203b8db63b377