evas_smart: Add a check for zero size before malloc

Summary:
	Size may be zero while allocating interfaces private data,
	when NULL is passed in EVAS_SMART_SUBCLASS_IFACE_NEW for ifaces argument.

	If size is 0, then malloc() returns either NULL, or a unique pointer
	value that can later be successfully passed to free(). It is implementation
	dependent. This case would be likely to occur in case of smart classes with
	no interfaces.

@fix

Signed-off-by: Vaibhav Gupta <g.vaibhav1@samsung.com>

Reviewers: raster, Hermet, tasn, cedric

Subscribers: SanghyeonLee, sachin.dev, singh.amitesh, cedric

Differential Revision: https://phab.enlightenment.org/D2679

src/lib/evas/canvas/evas_object_smart.c

@@ -496,6 +496,8 @@ _evas_smart_class_ifaces_private_data_alloc(Evas_Object *eo_obj,
           }
      }
 
+   if (!s->interfaces.size && !total_priv_sz) return;
+
    obj = eo_data_scope_get(eo_obj, MY_CLASS);
    obj->interface_privates = malloc(s->interfaces.size * sizeof(void *) + total_priv_sz);
    if (!obj->interface_privates)