Trash folder does not update the number of emails to be read after emptying

The Trash folder does not update the number of emails to be read after emptying

Steps to reproduce:

• set some emails (ex. 5) in the trash folder as "to read"
• to the right of the folder the number of emails to be read appears in bold (5)
• empty the entire trash folder: right click > empty

 Expected behaviour:

• the number of emails to be read disappears beside the folder

Actual behaviour:

• the number of e-mails to be read (5) remains set beside the folder

In order to arrange it is necessary to select reload tree.

Thanks to Federico Ballarini (Ref: #91902)