patch 8.1.1746: ":dl" is seen as ":dlist" instead of ":delete"

Problem:    ":dl" is seen as ":dlist" instead of ":delete".
Solution:   Do not use cmdidxs2[] if the length is 1. (closes #4721)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 3fa5129..f3a4eb7 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -3191,7 +3191,7 @@
 	if (ASCII_ISLOWER(eap->cmd[0]))
 	{
 	    int c1 = eap->cmd[0];
-	    int c2 = eap->cmd[1];
+	    int c2 = len == 1 ? NUL : eap->cmd[1];
 
 	    if (command_count != (int)CMD_SIZE)
 	    {