Fix #106366: Handle exceptions in add fur operator

Give errors in a few cases:
- The mesh has no UV map
- The faces have no area
- The applied modifier has no curve data (it may have been modified)

Use errors instead of cancelling the operator completely so the
operator can still do something useful when many meshes are
selected and only some fail.

Pull Request: https://projects.blender.org/blender/blender/pulls/106823

scripts/startup/bl_operators/object_quick_effects.py

@@ -121,8 +121,16 @@ class QuickFur(ObjectModeOperator, Operator):
 
         material = bpy.data.materials.new("Fur Material")
 
+        mesh_with_zero_area = False
+        mesh_missing_uv_map = False
+        modifier_apply_error = False
+
         for mesh_object in mesh_objects:
             mesh = mesh_object.data
+            if len(mesh.uv_layers) == 0:
+                mesh_missing_uv_map = True
+                continue
+
             with context.temp_override(active_object=mesh_object):
                 bpy.ops.object.curves_empty_hair_add()
             curves_object = context.active_object
@@ -132,7 +140,11 @@ class QuickFur(ObjectModeOperator, Operator):
             area = 0.0
             for poly in mesh.polygons:
                 area += poly.area
-            density = count / area
+            if area == 0.0:
+                mesh_with_zero_area = True
+                density = 10
+            else:
+                density = count / area
 
             generate_modifier = curves_object.modifiers.new(name="Generate", type='NODES')
             generate_modifier.node_group = generate_group
@@ -166,7 +178,10 @@ class QuickFur(ObjectModeOperator, Operator):
 
             if self.apply_hair_guides:
                 with context.temp_override(object=curves_object):
-                    bpy.ops.object.modifier_apply(modifier=generate_modifier.name)
+                    try:
+                        bpy.ops.object.modifier_apply(modifier=generate_modifier.name)
+                    except:
+                        modifier_apply_error = True
 
             curves_object.modifiers.move(0, len(curves_object.modifiers) - 1)
 
@@ -174,6 +189,13 @@ class QuickFur(ObjectModeOperator, Operator):
             for modifier in curves_object.modifiers:
                 modifier.node_group = modifier.node_group
 
+        if mesh_with_zero_area:
+            self.report({'WARNING'}, "Mesh has no face area")
+        if mesh_missing_uv_map:
+            self.report({'WARNING'}, "Mesh UV map required")
+        if modifier_apply_error and not mesh_with_zero_area:
+            self.report({'WARNING'}, "Unable to apply \"Generate\" modifier")
+
         return {'FINISHED'}