update to fix analysis panel freeze

[wotey]

This pull request includes several changes to the AnalysisPanel component in app/frontend/src/components/AnalysisPanel/AnalysisPanel.tsx to improve error handling and ensure the proper handling of undefined values. The most important changes include adding error messages for undefined values and ensuring the proper execution of asynchronous functions.

Improvements to error handling:

• Added error messages when sourceFileUrl is undefined and ensured setIsFetchingSourceFileBlob(false) is called in this case.
• Added warnings when activeCitation is undefined and set setActiveCitationObj(undefined) accordingly.
• Added error messages when sourceFile is undefined and threw errors when citationURL is undefined in the fetchMarkdownContent and fetchPlainTextContent functions.

Ensuring proper execution of asynchronous functions:

• Modified the fetchSourceFileBlob function to check for undefined sourceFile and ensure proper asynchronous execution.

Other changes:

• Updated the iframe source URL to handle pageNumber being null or undefined by using the nullish coalescing operator.

Fixes #904