Stop trying to access standard layer items when in multi-layer mode.
Merge pull request #1799 from fontforge/multilayer_charview_crash_1

Stop trying to access standard layer items when in multi-layer mode.
Fix a slight error in refiguring of cubic splines that caused them to fail to flag as linear.
Merge pull request #1802 from fontforge/allow_conversion_to_linear_1

Fix linearization of cubic splines.
Update osx folder error message