patch 8.0.0919: cursor color isn't set on startup

Problem:    Cursor color isn't set on startup.
Solution:   Initialize showing_mode to invalid value.
diff --git a/src/term.c b/src/term.c
index 80545ad..d72f58c 100644
--- a/src/term.c
+++ b/src/term.c
@@ -3670,7 +3670,7 @@
     void
 term_cursor_mode(int forced)
 {
-    static int showing_mode = NORMAL;
+    static int showing_mode = -1;
     char_u *p;
 
     /* Only do something when redrawing the screen and we can restore the