effects/colorpicker: Fix picking colors
Due to the wrong buffer format, the function failed with GL_INVALID_OPERATION error, which was silently ignored by the effect. It resulted in the constant phantom color being returned over and over again.
Co-Authored-By: David Edmundson kde@davidedmundson.co.uk BUG: 454974 FIXED-IN: 5.24.7, 5.25.4, 5.26
(cherry picked from commit df6331b6)