[FIX] hr_work_entry_contract: Fix work entry generation cron

Purpose
=======

The cron is breaking (expected singleton error) if treating contracts
from the same company at the same time.

Actually, this shouldn't be done that way to avoid mixing unrelated
resource.calendar.leave.

Handle the contracts over 2 cron execution instead.

addons/hr_work_entry_contract/models/hr_contract.py

@@ -388,6 +388,12 @@ class HrContract(models.Model):
             (not c.last_generation_date or c.last_generation_date < today))
         if not contracts_todo:
             return
+        countract_todo_count = len(contracts_todo)
+        # Filter contracts by company, work entries generation is not supposed to be called on
+        # contracts from differents companies, as we will retrieve the resource.calendar.leave
+        # and we don't want to mix everything up. The other contracts will be treated when the
+        # cron is re-triggered
+        contracts_todo = contracts_todo.filtered(lambda c: c.company_id == contracts_todo[0].company_id)
         # generate a batch of work entries
         BATCH_SIZE = 100
         # Since attendance based are more volatile for their work entries generation
@@ -398,5 +404,5 @@ class HrContract(models.Model):
         contracts_todo = contracts_todo.sorted(key=lambda c: 1 if c.has_static_work_entries() else 100)
         contracts_todo[:BATCH_SIZE]._generate_work_entries(start, stop, False)
         # if necessary, retrigger the cron to generate more work entries
-        if len(contracts_todo) > BATCH_SIZE:
+        if countract_todo_count > BATCH_SIZE:
             self.env.ref('hr_work_entry_contract.ir_cron_generate_missing_work_entries')._trigger()