Correct depth unit for BSB charts with UN=Meter (FS#1061)
(cherry picked from commit 0f1d8d2dcfa7621c57ee8823382f5304ae420e24)
Correct for potential crash on wheel zoom before app is fully initialized.
(cherry picked from commit 2a5b039521435c85c7351225949b0cd59ec77463)

Conflicts:
	src/Quilt.cpp
	src/chcanv.cpp