Pass native pointers to bases in the generated C#

Signed-off-by: Dimitar Dobrev <dpldobrev@protonmail.com>

src/Generator/Generators/CSharp/CSharpSources.cs

@@ -2186,7 +2186,7 @@ namespace CppSharp.Generators.CSharp
 
             var hasBaseClass = @class.HasBaseClass && @class.BaseClass.IsRefType;
             if (hasBaseClass)
-                WriteLineIndent(": base((void*) null)", @class.BaseClass.Visit(TypePrinter));
+                WriteLineIndent(": base((void*) native)", @class.BaseClass.Visit(TypePrinter));
 
             WriteOpenBraceAndIndent();
 
@@ -2195,15 +2195,15 @@ namespace CppSharp.Generators.CSharp
                 if (@class.BaseClass?.Layout.HasSubclassAtNonZeroOffset == true)
                     WriteLine("{0} = {1};", Helpers.PrimaryBaseOffsetIdentifier,
                         GetOffsetToBase(@class, @class.BaseClass));
-                if (!@class.IsAbstractImpl)
+                var hasVTables = @class.IsDynamic && GetUniqueVTableMethodEntries(@class).Count > 0;
+                if (!hasBaseClass || hasVTables)
                 {
                     WriteLine("if (native == null)");
                     WriteLineIndent("return;");
+                    if (!hasBaseClass)
+                        WriteLine($"{Helpers.InstanceIdentifier} = new global::System.IntPtr(native);");
                 }
-
-                WriteLine("{0} = new global::System.IntPtr(native);", Helpers.InstanceIdentifier);
                 var dtor = @class.Destructors.FirstOrDefault();
-                var hasVTables = @class.IsDynamic && GetUniqueVTableMethodEntries(@class).Count > 0;
                 var setupVTables = !@class.IsAbstractImpl && hasVTables && dtor?.IsVirtual == true;
                 if (setupVTables)
                 {
@@ -2223,7 +2223,7 @@ namespace CppSharp.Generators.CSharp
                     Unindent();
                 }
             }
-            else
+            else if (!hasBaseClass)
             {
                 WriteLine($"{Helpers.InstanceField} = *({TypePrinter.PrintNative(@class)}*) native;");
             }