patch 8.0.1544: when using 'termguicolors' SpellBad doesn't show
Problem: When using 'termguicolors' SpellBad doesn't show.
Solution: When the GUI colors are not set fall back to the cterm colors.
diff --git a/src/gui.h b/src/gui.h
index cca1ee3..b63125b 100644
--- a/src/gui.h
+++ b/src/gui.h
@@ -207,6 +207,8 @@
#define INVALCOLOR (guicolor_T)-11111 /* number for invalid color; on 32 bit
displays there is a tiny chance this is an
actual color */
+#define CTERMCOLOR (guicolor_T)-11110 /* only used for cterm.bg_rgb and
+ cterm.fg_rgb: use cterm color */
#ifdef FEAT_GUI_GTK
typedef PangoFontDescription *GuiFont; /* handle for a GUI font */