fix(DicomTagBrowser): Check for null metadata.

[jbocce]

Context

Fixes: #5575

Changes & Results

Added a null check in the Dicom tag browser component.

Testing

See #5575

Might also be good to check other exports followed by use of the dicom tag browser.

Checklist

PR

• My Pull Request title is descriptive, accurate and follows the
  semantic-release format and guidelines.

Code

• My code has been well-documented (function documentation, inline comments,
  etc.)

Public Documentation Updates

• The documentation page has been updated as necessary for any public API
  additions or removals.

Tested Environment

System:
OS: Windows 11 10.0.26200
CPU: (20) x64 12th Gen Intel(R) Core(TM) i7-12700H
Memory: 8.80 GB / 31.68 GB
Binaries:
Node: 20.9.0 - C:\Users\joebo\AppData\Local\fnm_multishells\14456_1767626745599\node.EXE
Yarn: 1.22.22 - C:\Program Files (x86)\Yarn\bin\yarn.CMD
npm: 10.1.0 - C:\Users\joebo\AppData\Local\fnm_multishells\14456_1767626745599\npm.CMD
bun: 1.2.23 - C:\Users\joebo.bun\bin\bun.EXE
Browsers:
Chrome: 143.0.7499.170

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[aimee-ferreira]

Testing Completed - Verified that the DICOM Tag Browser opens and functions correctly with newly created SEG and RTSS objects. No new defects were found during the testing.