Image item of Webcam not displayed using the external access

[maxulm]

New bug checklist

• I updated the iOS openHAB app to the latest TestFlight version.
• I read the Contribution Guidelines
• I searched for existing GitHub issues

Describe the bug
Using an image item in the sitemap with a snapshot url (using the ipccam-addon) is not displayed by using the external uri.
Accessing the uri to the basic ui sitemap in the browser, the image is displayed.
Connecting via VPN or using the app being in the home network it also works.
To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
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App (please complete the following information):

• Version [e.g. 2.4.19 (1580410467)]

Smartphone (please complete the following information):

• Device: [e.g. iphone 12 Pro Max]

openHAB (please complete the following information):

• Version [e.g. 3,0,0]

Additional context
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