IONOS: fix(Viewer): fix image load error with number folder

[fracado]

Fixes a bug that a file cannot be opened if it is on the same level as a (shared) folder with a name that only contains numbers.
(Only happens with Firefox.)

Note: Very similar to nextcloud/photos#783

[bromiesTM]

review ok
I'd wait for a response/agreement to this thread before merging
nextcloud#2736 (comment)

[fracado]

review ok I'd wait for a response/agreement to this thread before merging nextcloud#2736 (comment)

As nextcloud#2735 has been merged now, I'd suggest we can safely merge this one as well.

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