Avoid overwrite last ip or user_agent with empty ones

tlaverdure/laravel-echo-server#546
In some cases request doesn'nt has `ipAddress` or `userAgent`, with this change it avoid overwrite the last reported data

Author: PaolaRuby

src/Illuminate/Session/DatabaseSessionHandler.php

@@ -234,10 +234,12 @@ protected function userId()
     protected function addRequestInformation(&$payload)
     {
         if ($this->container->bound('request')) {
-            $payload = array_merge($payload, [
-                'ip_address' => $this->ipAddress(),
-                'user_agent' => $this->userAgent(),
-            ]);
+            if ($this->ipAddress()) {
+                $payload['ip_address'] = $this->ipAddress();
+            }
+            if ($this->userAgent()) {
+                $payload['user_agent'] = $this->userAgent();
+            }
         }
 
         return $this;