Mark third party installs

app/src/main/java/eu/faircode/email/ActivityBilling.java

@@ -200,7 +200,8 @@ abstract class ActivityBilling extends ActivityBase implements PurchasesUpdatedL
         if (purchases != null) {
             SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
             SharedPreferences.Editor editor = prefs.edit();
-            editor.remove("pro");
+            if (prefs.getBoolean("play_store", true))
+                editor.remove("pro");
             for (Purchase purchase : purchases) {
                 Log.i(Helper.TAG, "IAB SKU=" + purchase.getSku());
                 if ((BuildConfig.APPLICATION_ID + ".pro").equals(purchase.getSku())) {

app/src/main/java/eu/faircode/email/ActivityMain.java

@@ -23,6 +23,7 @@ import android.content.Intent;
 import android.content.SharedPreferences;
 import android.os.Bundle;
 import android.preference.PreferenceManager;
+import android.util.Log;
 
 import java.util.List;
 
@@ -42,6 +43,11 @@ public class ActivityMain extends AppCompatActivity implements FragmentManager.O
         SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
         prefs.registerOnSharedPreferenceChangeListener(this);
 
+        if (!Helper.isPlayStoreInstall(this)) {
+            Log.i(Helper.TAG, "Third party install");
+            prefs.edit().putBoolean("play_store", false).apply();
+        }
+
         if (prefs.getBoolean("eula", false)) {
             DB.getInstance(this).account().liveAccounts(true).observe(this, new Observer<List<EntityAccount>>() {
                 @Override