[FIX] base: ir field - set dependence as required when creating a com…

…pute field.

When you create a computed field, if you don't set the dependencies field
Odoo raises a traceback keyerror for ''.

Courtesy of @odony

openerp/addons/base/ir/ir_model_view.xml

@@ -269,7 +269,7 @@
                                         domain="[('ttype','=','serialized'), ('model_id', '=', model_id)]"
                                         attrs="{'readonly': [('state','=','base')]}"/>
                                     <field name="related"/>
-                                    <field name="depends"/>
+                                    <field name="depends" attrs="{'required': [('compute', '!=', False)] }"/>
                                     <field name="compute"/>
                                 </group>
                                 <h3>How to define a computed field</h3>