[FIX] web_filter_header_button: custom view compatibility

In custom views, like the reconciliation one, that use the control panel
we must prevent loading the FilterButton component.

TT49664

web_filter_header_button/static/src/control_panel/control_panel.xml

@@ -2,7 +2,7 @@
 <templates>
     <t t-inherit="web.Legacy.ControlPanel" t-inherit-mode="extension" owl="1">
         <xpath expr="//div[hasclass('o_cp_bottom')]" position="after">
-            <t t-if="env.view.type !== 'form'">
+            <t t-if="env.view and env.view.type !== 'form'">
                 <FilterButton />
             </t>
         </xpath>