[OZ: H-03] Incorrect calculations

[Robsonsjre]

We found the following instances of incorrect calculations in view functions that are not
currently called internally:

• In the previewWithdraw function, the DENOMINATOR over invertedFee is always bigger than 1 when the fee is non-zero. Hence, the final returned shares are always an
  overestimate. Further, the withdrawFeeRatio is multiplied to shares instead of
  assets as in other instances such as _getFee . Consider correcting the withdrawal
  fee calculation.

• The calculation in the assetsOf function over-estimates the actual commitment by an
  additional committedAssets . Consider removing the extra component.