Fix TimeSpan.MinValue overflow

Author: mythz

src/ServiceStack.Text/Support/TimeSpanConverter.cs

@@ -12,7 +12,7 @@ public static string ToXsdDuration(TimeSpan timeSpan)
 
             sb.Append(timeSpan.Ticks < 0 ? "-P" : "P");
 
-            double ticks = Math.Abs(timeSpan.Ticks);
+            double ticks = timeSpan.Ticks > 0 ? timeSpan.Ticks : timeSpan.Ticks * -1L;
             double totalSeconds = ticks / TimeSpan.TicksPerSecond;
             long wholeSeconds = (long) totalSeconds;
             long seconds = wholeSeconds;

tests/ServiceStack.Text.Tests/Issues/StackOverflowIssues.cs

@@ -0,0 +1,24 @@
+using System;
+using NUnit.Framework;
+
+namespace ServiceStack.Text.Tests.Issues
+{
+    public class StackOverflowIssues
+    {
+        public class MinTypes
+        {
+            public TimeSpan TimeSpan { get; set; }
+        }
+
+        [Test]
+        public void Can_convert_min_TimeSpan()
+        {
+            var c1 = new MinTypes {
+                TimeSpan = TimeSpan.MinValue,
+            };
+            var json = JsonSerializer.SerializeToString(c1, typeof(MinTypes));
+            var dto = JsonSerializer.SerializeToString(c1, typeof(MinTypes));
+            Assert.That(json, Is.EqualTo(dto));
+        }
+    }
+}