csharp: Add some null checks.

Summary:
- Check for nullness when getting stuff from C# to C
- We should return null when wrapping a NULL pointer instead of throwing
  an exception

Reviewers: felipealmeida, vitor.sousa, woohyun

Reviewed By: vitor.sousa

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D8580

src/bin/eolian_mono/eolian/mono/struct_definition.hh

@@ -48,7 +48,7 @@ struct to_internal_field_convert_generator
       if (klass)
         {
            if (!as_generator(
-                 indent << scope_tab << scope_tab << "_internal_struct." << string << " = _external_struct." << string << ".NativeHandle;\n")
+                 indent << scope_tab << scope_tab << "_internal_struct." << string << " = _external_struct." << string << "?.NativeHandle ?? System.IntPtr.Zero;\n")
                .generate(sink, std::make_tuple(field_name, field_name), context))
              return false;
         }
@@ -112,7 +112,7 @@ struct to_internal_field_convert_generator
       else if (field.type.c_type == "Eina_Value *" || field.type.c_type == "const Eina_Value *")
         {
            if (!as_generator(
-                 indent << scope_tab << scope_tab << "_internal_struct." << string << " = _external_struct." << string << ".NativeHandle;\n"
+                 indent << scope_tab << scope_tab << "_internal_struct." << string << " = _external_struct." << string << "?.NativeHandle ?? System.IntPtr.Zero;\n"
                ).generate(sink, std::make_tuple(field_name, field_name), context))
              return false;
         }

src/bindings/mono/eo_mono/iwrapper.cs

@@ -589,6 +589,12 @@ public class Globals
     /// <returns>The C# wrapper for this instance.</returns>
     public static Efl.Eo.IWrapper CreateWrapperFor(System.IntPtr handle, bool shouldIncRef=true)
     {
+
+        if (handle == IntPtr.Zero)
+        {
+            return null;
+        }
+
         IntPtr eoKlass = efl_class_get(handle);
 
         if (eoKlass == IntPtr.Zero)