Fix handling the response of the proxy

[nickvergessen]

      "Exception": "TypeError",
      "Message": "json_decode() expects parameter 1 to be string, object given",
      "Code": 0,
      "Trace": [
        {
          "file": "/var/www/html/apps/notifications/lib/Push.php",
          "line": 333,
          "function": "json_decode"
        },
        {
          "file": "/var/www/html/apps/notifications/lib/Push.php",
          "line": 124,
          "function": "sendNotificationsToProxies",
          "class": "OCA\\Notifications\\Push",
          "type": "->"
        },
        {
          "file": "/var/www/html/apps/notifications/lib/App.php",
          "line": 99,
          "function": "flushPayloads",
          "class": "OCA\\Notifications\\Push",
          "type": "->"
        },

[PVince81]

👍 makes sense

[nickvergessen]

Seems to have been a temporary error