Fix: #11905

[sachindigharra]

Fix # (see https://help.github.com/en/articles/closing-issues-using-keywords)

Describe changes proposed in this pull request:

• Handle the empty-list case in getDataAccessToken by creating, saving, and returning a new Data Access Token when the user has none
• Keep the existing behaviour for users with tokens by still returning the latest token from the list, preventing 500 errors while staying backward compatible

Checks

• The commit log is comprehensible. It follows 7 rules of great commit messages. We can fix this during merge by using a squash+merge if necessary
• Has tests or has a separate issue that describes the types of test that should be created. If no test is included it should explicitly be mentioned in the PR why there is no test.
• Is this PR adding logic based on one or more clinical attributes? If yes, please make sure validation for this attribute is also present in the data validation / data loading layers (in backend repo) and documented in File-Formats Clinical data section!
• Make sure your PR has one of the labels defined in https://github.com/cBioPortal/cbioportal/blob/master/.github/release-drafter.yml

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