avoid naming conflicts

Author: lbargaoanu

src/AutoMapper/Internal/TypeDetails.cs

@@ -48,7 +48,7 @@ void SetNameToMember()
                 }
                 foreach (var member in accessors)
                 {
-                    _nameToMember.Add(member.Name, member);
+                    _nameToMember.TryAdd(member.Name, member);
                     if (Config.Postfixes.Count == 0 && Config.Prefixes.Count == 0)
                     {
                         continue;

src/UnitTests/MemberResolution.cs

@@ -4,6 +4,34 @@
 using Xunit;
 namespace AutoMapper.UnitTests.MemberResolution;
 
+public class When_multiple_source_members_match_postfix : AutoMapperSpecBase
+{
+    class Order
+    {
+        public int ProductId { get; set; }
+        public Product Product { get; set; }
+    }
+
+    class OrderDto
+    {
+        public int ProductId { get; set; }
+    }
+    class Product
+    {
+        public int Id { get; set; }
+    }
+    protected override MapperConfiguration CreateConfiguration() => new(c =>
+    {
+        c.RecognizePostfixes("Id");
+        c.CreateMap<Order, OrderDto>();
+    });
+    [Fact]
+    public void Should_prefer_the_property()
+    {
+        var destination = Map<OrderDto>(new Order { ProductId = 12, Product = new() { Id = 42 } });
+        destination.ProductId.ShouldBe(12);
+    }
+}
 public class When_multiple_source_members_match : AutoMapperSpecBase
 {
     class Source