Bugfix Tools::CodeView2::GutterView - do not redraw gutter if its not shown. This actually fixes DNU when CodeView2 is used in diff view. Then the second gutter is not shown and #yOfTextViewLine: returns nil (bad) which leads to DNU.

syntax: glob
*.so
*.H
*.o
*.STH
*.sc
*.class
*Init.c
*.base
*.orig
*.local
*.other
st.chg
makefile
smallsense/makefile