"Open in new map... " option is broken

[Andreas Janz]

A new map view is opened, but without a layer in it.

Note that no error is printed in the console.

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[Andreas Janz]

@Benjamin Jakimow note that I already added new RGB visualizations (#976). So be sure to pull updates before fixing the isse.

[Andreas Janz]

Also note that the error already existed before I added new visualizations (confirmed by @Fabian Thiel ).

[Benjamin Jakimow]

resolves #1023

→ <<cset 496ede7557e9>>