[FIX] sale: Set default value for sales_count
[FIX] sale: Set default value for sales_count

Fixes https://github.com/odoo/odoo/issues/39431
Assigning default value for non-stored compute fields is required in 13.0

closes odoo/odoo#39468

X-original-commit: b00c9b982241d83f07e03b10851cc55884e3c2fc
Signed-off-by: Victor Feyens (vfe) <433cda6c0f0b5b2dac2ef769109a6da90db60157@odoo.com>

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