bad download jobs submitted to InstallManagerService

Reported by a large number of people in alpha7:

java.lang.RuntimeException: Unable to start service org.fdroid.fdroid.installer.InstallManagerService@a8719a7 with Intent {
act=org.fdroid.fdroid.InstallManagerService.action.INSTALL dat=https://f-droid.org/... cmp=org.fdroid.fdroid/.installer.InstallManagerService }:
java.lang.NullPointerException: Attempt to read from field 'java.lang.String org.fdroid.fdroid.data.Apk.packageName' on a null object reference
        at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3045)
        at android.app.ActivityThread.-wrap17(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1452)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:5443)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
Caused by: java.lang.NullPointerException: Attempt to read from field 'java.lang.String org.fdroid.fdroid.data.Apk.packageName' on a null object reference
        at org.fdroid.fdroid.installer.InstallManagerService.getAppDetailsIntent(InstallManagerService.java:277)
        at org.fdroid.fdroid.installer.InstallManagerService.createNotification(InstallManagerService.java:245)
        at org.fdroid.fdroid.installer.InstallManagerService.onStartCommand(InstallManagerService.java:138)
        at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3028)
        ... 8 more
java.lang.NullPointerException: Attempt to read from field 'java.lang.String org.fdroid.fdroid.data.Apk.packageName' on a null object reference
        at org.fdroid.fdroid.installer.InstallManagerService.getAppDetailsIntent(InstallManagerService.java:277)
        at org.fdroid.fdroid.installer.InstallManagerService.createNotification(InstallManagerService.java:245)
        at org.fdroid.fdroid.installer.InstallManagerService.onStartCommand(InstallManagerService.java:138)
        at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3028)
        at android.app.ActivityThread.-wrap17(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1452)
        [...]