Liquidity pool staking dialog not calculating share asset amount

**Describe the bug**
When asset A and B are both 0, upon entering an asset A amount the asset B amount is calculated, but the associated pool share amount is not distplayed.

**To Reproduce**

Go to pool staking, have 0 in both a and b fields.

Enter 1 in asset A.

Asset B will be calculated, but the pool share asset amount won't be.

**Expected behavior**

Calculate the pool share amount properly.

**Screenshots**


Start at the pool staking dialog and reproduce the case with both asset fields at 0, then enter 1 in asset A. Trace where the asset B amount is calculated and compare that flow with the pool share amount calculation. Done means the share asset amount is displayed correctly in this scenario.

Written by the indexing model from the issue text.