Adding changes to 3 files with code review findings

[ganeshkamath89]

1) Changing size to MI_Instance* in malloc instead of MI_Instance** 2) Setting handle inside AUTHORIZATION macro check as it is defined inside 3) Moving DISABLE_SHELL block above the call

[ganeshkamath89]

@microsoft-github-policy-service agree

[ganeshkamath89]

closing this pull request to request separate requests for each change