clang-tidy: Enable bugprone-unchecked-optional

Modified code to address issues flagged by
bugprone-unchecked-optional-access check.

Tested: Build and unit tests passed successfully.

Change-Id: Icd445afaf827f7c346e44dfe3ce9ba98374e176a
Signed-off-by: Jayanth Othayoth <ojayanth@gmail.com>