Don't create duplicate move

supply_on_sale could be changed between two calls on get_move so we must also
check if a purchase request is not yet created.

review857002
(transplanted from b8717ff3e5597d65046fb9da828b56a82d45b512)

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extra : transplant_source : %B8q%7F%F3%E5Y%7De%04o%B9%DA%82%8BV%A8-E%B5%12
Process sale also when processing purchase

If Purchase.process creates new stock moves, Sale.process must be called to
consider this new moves.

review858002
(transplanted from 5c867861be6e5e79aa0fec4e0dc9ad4afb243441)

--HG--
extra : transplant_source : %5C%86xa%BEn%5Ey%AA%0F%ECN%0D%C9%ADJ%FB%244A