Call TemporaryFileProvider.cleanup() in Handler

This *might* fix Samsung problems. Let's see if it reduces crash reports.

See also:
https://stackoverflow.com/questions/41474623/sporadic-illegalargumentexception-unknown-url-content

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/KeychainApplication.java

@@ -29,6 +29,7 @@ import android.graphics.Bitmap;
 import android.graphics.PorterDuff;
 import android.graphics.drawable.Drawable;
 import android.os.Build;
+import android.os.Handler;
 import android.support.annotation.Nullable;
 import android.widget.Toast;
 
@@ -115,7 +116,7 @@ public class KeychainApplication extends Application {
         TlsCertificatePinning.addPinnedCertificate("api.keybase.io", getAssets(), "api.keybase.io.CA.cer");
         TlsCertificatePinning.addPinnedCertificate("keyserver.ubuntu.com", getAssets(), "DigiCertGlobalRootCA.cer");
 
-        TemporaryFileProvider.cleanUp(this);
+        new Handler().post(() -> TemporaryFileProvider.cleanUp(getApplicationContext()));
     }
 
     /**

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/provider/TemporaryFileProvider.java

@@ -111,6 +111,7 @@ public class TemporaryFileProvider extends ContentProvider {
     }
 
     public static int cleanUp(Context context) {
+        Timber.d("Cleaning up temporary files…");
         return context.getContentResolver().delete(
                 CONTENT_URI,
                 TemporaryFileColumns.COLUMN_TIME + "< ?",