Fix NRE when calling Refresh() before static type initializers

Author: mythz

src/ServiceStack.Text/Json/JsonReader.Generic.cs

@@ -50,6 +50,9 @@ static JsonReader()
 
         public static void Refresh()
         {
+            if (JsonReader.Instance == null)
+                return;
+
             ReadFn = JsonReader.Instance.GetParseFn<T>();
         }
 

src/ServiceStack.Text/Json/JsonWriter.Generic.cs

@@ -154,7 +154,10 @@ public static void Reset()
 
 	    public static void Refresh()
 	    {
-	        CacheFn = typeof (T) == typeof (object)
+            if (JsonWriter.Instance == null)
+                return;
+
+	        CacheFn = typeof(T) == typeof(object)
 	            ? JsonWriter.WriteLateBoundObject
 	            : JsonWriter.Instance.GetWriteFn<T>();
 	    }

src/ServiceStack.Text/Jsv/JsvReader.Generic.cs

@@ -50,6 +50,9 @@ static JsvReader()
 
         public static void Refresh()
         {
+            if (JsvReader.Instance == null)
+                return;
+
             ReadFn = JsvReader.Instance.GetParseFn<T>();
         }
 

src/ServiceStack.Text/Jsv/JsvWriter.Generic.cs

@@ -112,7 +112,10 @@ public static void Reset()
 
 	    public static void Refresh()
 	    {
-	        CacheFn = typeof (T) == typeof (object)
+            if (JsvWriter.Instance == null)
+                return;
+
+            CacheFn = typeof(T) == typeof(object)
 	            ? JsvWriter.WriteLateBoundObject
 	            : JsvWriter.Instance.GetWriteFn<T>();
 	    }