Fixes loading error when using wado-uri to load a volume

[jmhmd]

Context

In the case of loading a new volume with WADO-URI, we may not have loaded
metadata for all imageIds, as they are streaming in. The
getViewReference() call uses getClosestImageId() in its call stack, which
will error in that scenario as it tries to loop over all imageId
metadata. So only call getViewReference if necessary.

Changes & Results

Removes unnecessary function call that errors in specific scenarios.

Testing

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

• [] "OS:
• [] "Node version:
• [] "Browser:

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