Mojo cpp bindings: remove redundant validation in Decode*().

mojo/public/tools/bindings/generators/cpp_templates/struct_macros.tmpl

Index: mojo/public/tools/bindings/generators/cpp_templates/struct_macros.tmpl
diff --git a/mojo/public/tools/bindings/generators/cpp_templates/struct_macros.tmpl b/mojo/public/tools/bindings/generators/cpp_templates/struct_macros.tmpl
index 1897a4924a792e6ed53f184843b88fdf0303b4b1..4d586f7631ac1c03315abbc5bd451fee709c2a0a 100644
--- a/mojo/public/tools/bindings/generators/cpp_templates/struct_macros.tmpl
+++ b/mojo/public/tools/bindings/generators/cpp_templates/struct_macros.tmpl
@@ -78,12 +78,9 @@ mojo::internal::EncodeHandle(&{{pf.field.name}}, handles);
 
 {%- macro decodes(struct) -%}
 {%-   for pf in struct.packed.packed_fields if pf.field.kind|is_object_kind -%}
-if (!mojo::internal::Decode(&{{pf.field.name}}, message))
-  return false;
+mojo::internal::Decode(&{{pf.field.name}}, handles);
 {%    endfor %}
 {%-   for pf in struct.packed.packed_fields if pf.field.kind|is_handle_kind -%}
-if (!mojo::internal::DecodeHandle(&{{pf.field.name}},
-                                  message->mutable_handles()))
-  return false;
+mojo::internal::DecodeHandle(&{{pf.field.name}}, handles);
 {%    endfor %}
 {%- endmacro -%}