To reproduce the issue:
1. Create a product:
   - Type: Storable
   - Category:
     - Costing Method: AVCO
2. IN 2 @ 4.63/u
3. IN 5 @ 3.04/u
4. OUT 0.1
5. Repeat step 4 70 time in total, so that the final quantity is 0
6. Open the inventory valuation of the product

Error: the total value is $-0.04 instead of $0.
The compensation of rounding issue is stuck by a check that ensure we don't erase a valuation error.

However, this check can never succeed with small quantities, here is the mathematical proof:
°Current check: rounding_error <= qty * curr_rounding / 2
With:
1) rounding_error >= curr_rounding
2) 0 < qty < 2
3) v1 = rounding_error / curr_rounding
4) v2 = qty / 2
We can be sure that:
5) v1 >= 1 because of 1)
6) v2 < 1 because of 2)
7) v1 > v2 because of 5) and 6)

° rounding_error <= qty * curr_rounding / 2
° rounding_error * curr_rounding <= qty * curr_rounding / 2 * curr_rounding
° rounding_error / curr_rounding <= qty / 2
° v1 <= v2
==>> This contradict 7), hence this check can never be True for qty < 2

To fix this issue, we change the check to:
 ° rounding_error <= qty * curr_rounding / 2 OR rounding_error <= curr_rounding
 Where the 1st part doesn't change, but the second one is true when rounding_error == curr_rounding

closes odoo/odoo#115606

X-original-commit: a76fb7ff
Signed-off-by: William Henrotin (whe) <whe@odoo.com>
Signed-off-by: David <dafr@odoo.com>