Wrong calculation of solvency after request to close and after close position
`isSolventAfterClosePosition` and `isSolventAfterRequestToClosePosition` do not account for the extra profit that the user would get from closing the position.\\nWhen a party A creates a request for closing a position, the `isSolventAfterRequestToClosePosition` function is called to check if the user is solvent after the request. In the same way, when someone tries to close a position, the `isSolventAfterClosePosition` function is called to check if both party A and party B are solvent after closing the position.\\nBoth functions calculate the available balance for party A and party B, and revert if it is lower than zero. After that, the function accounts for the the extra loss that the user would get as a result of the difference between `closePrice` and `upnlSig.price`, and checks if the user is solvent after that.\\nThe problem is that the function does not account for the opposite case, that is the case where the user would get an extra profit as a result of the difference between `closePrice` and `upnlSig.price`. This means that the user would not be able to close the position, even if at the end of the transaction they would be solvent.\\nProof of Concept\\nThere is an open position with:\\nPosition type: LONG\\nQuantity: 1\\nLocked: 50\\nOpened price: 100\\nCurrent price: 110\\nQuote position uPnL Party A: 10\\nParty B calls `fillCloseRequest` with:\\nClosed price: 120\\nIn `isSolventAfterClosePosition` the following is calculated:\\n```\\npartyAAvailableBalance = freeBalance + upnl + unlockedAmount = -5\\n```\\n\\nAnd it reverts on:\\n```\\nrequire(\\n    partyBAvailableBalance >= 0 && partyAAvailableBalance >= 0,\\n    "LibSolvency: Available balance is lower than zero"\\n);\\n```\\n\\nHowever, the extra profit for `closedPrice - upnlSig.price = 120 - 110 = 10` is not accounted for in the `partyAAvailableBalance` calculation, that should be `partyAAvailableBalance = - 5 + 10 = 5`. Party A would be solvent after closing the position, but the transaction reverts.
Add the extra profit to the `partyAAvailableBalance` calculation.
In a situation where the difference between the closed price and the current price will make the user solvent, users will not be able to close their positions, even if at the end of the transaction they would be solvent.
```\\npartyAAvailableBalance = freeBalance + upnl + unlockedAmount = -5\\n```\\n