fix(subsonic): make Share's lastVisited optional

Signed-off-by: Deluan <deluan@navidrome.org>

server/subsonic/responses/.snapshots/Responses Shares with data should match .JSON

@@ -49,9 +49,9 @@
         "url": "http://localhost/p/ABC123",
         "description": "Check it out!",
         "username": "deluan",
-        "created": "0001-01-01T00:00:00Z",
-        "expires": "0001-01-01T00:00:00Z",
-        "lastVisited": "0001-01-01T00:00:00Z",
+        "created": "2016-03-02T20:30:00Z",
+        "expires": "2016-03-02T20:30:00Z",
+        "lastVisited": "2016-03-02T20:30:00Z",
         "visitCount": 2
       }
     ]

server/subsonic/responses/.snapshots/Responses Shares with data should match .XML

@@ -1,6 +1,6 @@
 <subsonic-response xmlns="http://subsonic.org/restapi" status="ok" version="1.8.0" type="navidrome" serverVersion="v0.0.0" openSubsonic="true">
   <shares>
-    <share id="ABC123" url="http://localhost/p/ABC123" description="Check it out!" username="deluan" created="0001-01-01T00:00:00Z" expires="0001-01-01T00:00:00Z" lastVisited="0001-01-01T00:00:00Z" visitCount="2">
+    <share id="ABC123" url="http://localhost/p/ABC123" description="Check it out!" username="deluan" created="2016-03-02T20:30:00Z" expires="2016-03-02T20:30:00Z" lastVisited="2016-03-02T20:30:00Z" visitCount="2">
       <entry id="1" isDir="false" title="title" album="album" artist="artist" duration="120" isVideo="false" bpm="0" comment="" sortName="" mediaType="" musicBrainzId="" channelCount="0" samplingRate="0">
         <replayGain></replayGain>
       </entry>

server/subsonic/responses/.snapshots/Responses Shares with only required fields should match .JSON

@@ -0,0 +1,18 @@
+{
+  "status": "ok",
+  "version": "1.8.0",
+  "type": "navidrome",
+  "serverVersion": "v0.0.0",
+  "openSubsonic": true,
+  "shares": {
+    "share": [
+      {
+        "id": "ABC123",
+        "url": "http://localhost/s/ABC123",
+        "username": "johndoe",
+        "created": "2016-03-02T20:30:00Z",
+        "visitCount": 1
+      }
+    ]
+  }
+}

server/subsonic/responses/.snapshots/Responses Shares with only required fields should match .XML

@@ -0,0 +1,5 @@
+<subsonic-response xmlns="http://subsonic.org/restapi" status="ok" version="1.8.0" type="navidrome" serverVersion="v0.0.0" openSubsonic="true">
+  <shares>
+    <share id="ABC123" url="http://localhost/s/ABC123" username="johndoe" created="2016-03-02T20:30:00Z" visitCount="1"></share>
+  </shares>
+</subsonic-response>