create branch 2.6

--HG--
branch : 2.6
Fix get_invoice_state

When there are invoice lines, the state should be waiting.

issue3723
review3961002
(grafted from 2120885915659d7654206232ac76e3cf5afecc80)

--HG--
branch : 2.6
extra : source : 2120885915659d7654206232ac76e3cf5afecc80