Call Looper.prepareMainLooper() to avoid exception

Some devices internally create a Handler when creating an input Surface,
causing an exception:

> Surface: java.lang.RuntimeException: Can't create handler inside
> thread that has not called Looper.prepare()

As a workaround, call Looper.prepareMainLooper() beforehand.

Fixes:
 - <https://github.com/Genymobile/scrcpy/issues/240>
 - <https://github.com/Genymobile/scrcpy/issues/921>

Signed-off-by: Romain Vimont <rom@rom1v.com>

server/src/main/java/com/genymobile/scrcpy/ScreenEncoder.java

@@ -7,6 +7,7 @@ import android.media.MediaCodec;
 import android.media.MediaCodecInfo;
 import android.media.MediaFormat;
 import android.os.IBinder;
+import android.os.Looper;
 import android.view.Surface;
 
 import java.io.FileDescriptor;
@@ -54,6 +55,16 @@ public class ScreenEncoder implements Device.RotationListener {
     }
 
     public void streamScreen(Device device, FileDescriptor fd) throws IOException {
+        // Some devices internally create a Handler when creating an input Surface, causing an exception:
+        //   "Can't create handler inside thread that has not called Looper.prepare()"
+        // <https://github.com/Genymobile/scrcpy/issues/240>
+        //
+        // Use Looper.prepareMainLooper() instead of Looper.prepare() to avoid a NullPointerException:
+        //   "Attempt to read from field 'android.os.MessageQueue android.os.Looper.mQueue'
+        //    on a null object reference"
+        // <https://github.com/Genymobile/scrcpy/issues/921>
+        Looper.prepareMainLooper();
+
         MediaFormat format = createFormat(bitRate, frameRate, iFrameInterval);
         device.setRotationListener(this);
         boolean alive;