Unnecessary array boundaries check when loading an array element twice

[code423n4]

Handle

robee

Vulnerability details

There are places in the code (especially in for-each loops) that loads the same array element more
than once. In such cases, only one array boundaries check should take place, and the rest are unnecessary.
Therefore, this array element should be cached in a local variable and then be loaded
again using this local variable, skipping the redundent second array boundaries check:

    CreditLine.sol, variable name: _strategyList times: 2 at: _withdrawBorrowAmount
    CreditLine.sol, variable name: _strategyList times: 2 at: _repayFromSavingsAccount
    CreditLine.sol, variable name: _strategyList times: 3 at: _transferCollateral
    SavingsAccount.sol, variable name: _strategyList times: 2 at: withdrawAll

[ritik99]

Duplicate of #157

[0xean]

not a duplicate of #157 - different suggestion regarding index.