patch 9.0.0886: horizontal mouse scroll only works in the GUI

Problem:    Horizontal mouse scroll only works in the GUI.
Solution:   Make horizontal mouse scroll also work in a terminal.
            (Christopher Plewright, closes #11448)
diff --git a/src/normal.c b/src/normal.c
index 7b47f18..79f1686 100644
--- a/src/normal.c
+++ b/src/normal.c
@@ -3047,7 +3047,7 @@
 	clearopbeep(cap->oap);
 
     // Even if an operator was pending, we still want to scroll
-    gui_do_horiz_scroll(scrollbar_value, FALSE);
+    do_mousescroll_horiz(scrollbar_value);
 }
 #endif