Digikam git build without marble issue

[leoutation at gmx.fr]

Hi
Usually,  I successfully build Digikam git without marble because it's
optional.
I see now Digikam build process strangely finds libmarble on my system
but i don't have any 'marble' package/library installed on my system
  libmarble found.......................... YES (optional)

I think it's a bug
conditions: Arch system QT5 KF5

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Maderios