[5.x] Fix Custom Set Icons not working if path contains a dot (.)

[andjsch]

This PR fixes an issue with the svg-icon component not showing the icon if the path contains a dot somewhere.

In my case, the site directory on the staging server is the name of the full domain, which of course, contains a dot. E.g. example.com.

The global helper function data_get() splits strings by . leading the function to not work as expected.

fixes #11864

[andjsch]

Here's the before:

and here the after: