Fixed possible resource leak in AndroidFileHandle::length()

This leak was reported by following exception when application was executed with Strict Mode enabled:

<pre>
E/StrictMode(9784): A resource was acquired at attached stack trace but never released. See java.io.Closeable for information on avoiding resource leaks.
E/StrictMode(9784): java.lang.Throwable: Explicit termination method 'close' not called
E/StrictMode(9784): 	at dalvik.system.CloseGuard.open(CloseGuard.java:184)
E/StrictMode(9784): 	at android.os.ParcelFileDescriptor.<init>(ParcelFileDescriptor.java:412)
E/StrictMode(9784): 	at android.content.res.AssetManager.openAssetFd(Native Method)
E/StrictMode(9784): 	at android.content.res.AssetManager.openFd(AssetManager.java:331)
E/StrictMode(9784): 	at com.badlogic.gdx.backends.android.AndroidFileHandle.length(AndroidFileHandle.java:151)
E/StrictMode(9784): 	at com.badlogic.gdx.files.FileHandle.readBytes(FileHandle.java:215)
E/StrictMode(9784): 	at com.badlogic.gdx.graphics.Pixmap.<init>(Pixmap.java:137)
E/StrictMode(9784): 	at com.kreymerman.alfred.graphics.loaders.TextureLoader.loadTextureData(TextureLoader.java:59)
E/StrictMode(9784): 	at com.kreymerman.alfred.graphics.loaders.TextureLoader.load(TextureLoader.java:45)
E/StrictMode(9784): 	at com.kreymerman.alfred.graphics.loaders.TextureLoader.load(TextureLoader.java:36)
E/StrictMode(9784): 	at com.kreymerman.alfred.graphics.loaders.TextureLoader.loadOverlay(TextureLoader.java:30)
E/StrictMode(9784): 	at com.kreymerman.alfred.game.LoadingScreen.createScreenResources(LoadingScreen.java:122)
E/StrictMode(9784): 	at com.kreymerman.alfred.game.ScreenManager.finishResourceLoading(ScreenManager.java:222)
E/StrictMode(9784): 	at com.kreymerman.alfred.game.ScreenManager.switchToScreenAsync(ScreenManager.java:198)
E/StrictMode(9784): 	at com.kreymerman.alfred.game.ScreenManager.switchToScreenAsync(ScreenManager.java:135)
E/StrictMode(9784): 	at com.kreymerman.alfred.SplashScreen.render(SplashScreen.java:98)
E/StrictMode(9784): 	at com.kreymerman.alfred.game.Game.render(Game.java:164)
E/StrictMode(9784): 	at com.badlogic.gdx.backends.android.AndroidGraphics.onDrawFrame(AndroidGraphics.java:449)
E/StrictMode(9784): 	at android.opengl.GLSurfaceView$GLThread.guardedRun(GLSurfaceView.java:1516)
E/StrictMode(9784): 	at android.opengl.GLSurfaceView$GLThread.run(GLSurfaceView.java:1240)
</pre>