patch 9.1.0475: cmod_split modifier is always reset in term_start()

Problem:  cmod_split modifier is always reset in term_start()
Solution: only clear the WSP_VERT flag, if it is not already in
          cmdmod.cmod_split (Yegappan Lakshmanan)

closes: #14961

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/terminal.c b/src/terminal.c
index 28e1abf..07b69c6 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -541,11 +541,12 @@
 	int cmod_split_modified = FALSE;
 	if (vertical)
 	{
+	    if (!(cmdmod.cmod_split & WSP_VERT))
+		cmod_split_modified = TRUE;
 	    cmdmod.cmod_split |= WSP_VERT;
-	    cmod_split_modified = TRUE;
 	}
 	ex_splitview(&split_ea);
-	if (vertical && cmod_split_modified)
+	if (cmod_split_modified)
 	    cmdmod.cmod_split &= ~WSP_VERT;
 	if (curwin == old_curwin)
 	{