GPencil: Material panel is hidden after adding new material

This bug was introduced by previous Pin fix commit. Maybe it's not the best solution, but this bug is critical and need a quick fix.

This commit fix the problem, but not totally sure this is working fine with pin.

@dfelinto Could you review and adapt if required.

1 files changed, 8 insertions, 1 deletions

diff --git a/release/scripts/startup/bl_ui/properties_material_gpencil.py b/release/scripts/startup/bl_ui/properties_material_gpencil.py
index a27d2ff9b84..22fa8dee65b 100644
--- a/release/scripts/startup/bl_ui/properties_material_gpencil.py
+++ b/release/scripts/startup/bl_ui/properties_material_gpencil.py
@@ -85,13 +85,20 @@ class GPMaterialButtonsPanel:
         return ma and ma.grease_pencil
 
 
-class MATERIAL_PT_gpencil_slots(GreasePencilMaterialsPanel, GPMaterialButtonsPanel, Panel):
+class MATERIAL_PT_gpencil_slots(GreasePencilMaterialsPanel, Panel):
     bl_label = "Grease Pencil Material Slots"
     bl_space_type = 'PROPERTIES'
     bl_region_type = 'WINDOW'
     bl_context = "material"
     bl_options = {'HIDE_HEADER'}
 
+    @classmethod
+    def poll(cls, context):
+        ob = context.object
+        ma = context.material
+
+        return (ma and ma.grease_pencil) or (ob and ob.type == 'GPENCIL')
+
 
 # Used as parent for "Stroke" and "Fill" panels
 class MATERIAL_PT_gpencil_surface(GPMaterialButtonsPanel, Panel):