Hans-Christoph Steiner 5523a443f8 never have null Apks in InstallManagerService
In order to avoid having null guards making the code ugly, use a "blank"
instance of Apk which will work for the various comparisons.  This fixes
this crash:

fixes #688

java.lang.NullPointerException
	at org.fdroid.fdroid.installer.InstallManagerService$4.onReceive(InstallManagerService.java:243)
	at android.support.v4.content.LocalBroadcastManager.executePendingBroadcasts(LocalBroadcastManager.java:297)
	at android.support.v4.content.LocalBroadcastManager.access$000(LocalBroadcastManager.java:46)
	at android.support.v4.content.LocalBroadcastManager$1.handleMessage(LocalBroadcastManager.java:116)
	at android.os.Handler.dispatchMessage(Handler.java:102)
	at android.os.Looper.loop(Looper.java:136)
	at android.app.ActivityThread.main(ActivityThread.java:5001)
	at java.lang.reflect.Method.invokeNative(Native Method)
	at java.lang.reflect.Method.invoke(Method.java:515)
	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
	at dalvik.system.NativeStart.main(Native Method)
2016-06-16 16:50:29 +02:00
..