housekeeping: Handle the DateTimeOffset cause where BSON data is alre…

…ady in Date. (#450)

Handle backwards compatibility case where data is already stored in the old format in the BSON format.

src/Akavache.Core/JsonDateTimeOffsetTickConverter.cs

@@ -19,6 +19,11 @@ public override void WriteJson(JsonWriter writer, object value, JsonSerializer s
 
         public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
         {
+            if (reader.TokenType == JsonToken.Date)
+            {
+                return (DateTimeOffset)reader.Value;
+            }
+
             var data = serializer.Deserialize<DateTimeOffsetData>(reader);
 
             if (data == null)