ui,prefs: set db in-memory name correctly

Instead of :memory:, use file::memory:

Related: #1030

ui/opensnitch/dialogs/preferences.py

@@ -519,15 +519,18 @@ def _save_db_config(self):
 
         if self.comboDBType.currentIndex() != Database.DB_TYPE_MEMORY:
             if self.dbLabel.text() != "":
-                self._cfg.setSettings(Config.DEFAULT_DB_FILE_KEY, self.dbLabel.text())
+                db_name = self.dbLabel.text()
             else:
                 Message.ok(
                     QC.translate("preferences", "Warning"),
                     QC.translate("preferences", "You must select a file for the database<br>or choose \"In memory\" type."),
                     QtWidgets.QMessageBox.Warning)
                 self.dbLabel.setText("")
                 return False
+        else:
+            db_name = Database.DB_IN_MEMORY
 
+        self._cfg.setSettings(Config.DEFAULT_DB_FILE_KEY, db_name)
         self._cfg.setSettings(Config.DEFAULT_DB_TYPE_KEY, dbtype)
         self._cfg.setSettings(Config.DEFAULT_DB_PURGE_OLDEST, bool(self.checkDBMaxDays.isChecked()))
         self._cfg.setSettings(Config.DEFAULT_DB_MAX_DAYS, int(self.spinDBMaxDays.value()))