fix: fix an issue when the media preview is not a string

[jeremydw]

Not sure if this is the right fix but it guards against the crash.

Fixes this error:

Uncaught TypeError: e.path.startsWith is not a function
    at u.get previewUrl [as previewUrl] (app.min.js?fingerprint=2f9b7d317dbae006e7bc3da2a168810f:formatted:50873)
    at u.templatePreviewMedia (app.min.js?fingerprint=2f9b7d317dbae006e7bc3da2a168810f:formatted:50979)
    at l.templateCollapsed (app.min.js?fingerprint=2f9b7d317dbae006e7bc3da2a168810f:formatted:51306)
    at l.template (app.min.js?fingerprint=2f9b7d317dbae006e7bc3da2a168810f:formatted:51260)
    at app.min.js?fingerprint=2f9b7d317dbae006e7bc3da2a168810f:formatted:51228
    at app.min.js?fingerprint=2f9b7d317dbae006e7bc3da2a168810f:formatted:35794
    at f.commit (app.min.js?fingerprint=2f9b7d317dbae006e7bc3da2a168810f:formatted:36134)
    at o.update (app.min.js?fingerprint=2f9b7d317dbae006e7bc3da2a168810f:formatted:36309)
    at f.__commitTemplateResult (app.min.js?fingerprint=2f9b7d317dbae006e7bc3da2a168810f:formatted:36161)
    at f.commit (app.min.js?fingerprint=2f9b7d317dbae006e7bc3da2a168810f:formatted:36137)

Value of e.path here is:

_data: "/assets/assets.yaml?howSearchWorks3_small.url"
_type: "pod.yaml"