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)

src/ex_docmd.c

@@ -3191,7 +3191,7 @@ find_command(exarg_T *eap, int *full UNUSED)
 	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)
 	    {

src/testdir/Make_all.mak

@@ -106,6 +106,7 @@ NEW_TESTS = \
 	test_ex_equal \
 	test_ex_undo \
 	test_ex_z \
+	test_excmd \
 	test_exec_while_if \
 	test_execute_func \
 	test_exists \
@@ -328,6 +329,7 @@ NEW_TESTS_RES = \
 	test_erasebackword.res \
 	test_escaped_glob.res \
 	test_eval_stuff.res \
+	test_excmd.res \
 	test_exec_while_if.res \
 	test_exists.res \
 	test_exists_autocmd.res \

src/testdir/test_excmd.vim

@@ -0,0 +1,10 @@
+" Tests for various Ex commands.
+
+func Test_ex_delete()
+  new
+  call setline(1, ['a', 'b', 'c'])
+  2
+  " :dl is :delete with the "l" flag, not :dlist
+  .dl
+  call assert_equal(['a', 'c'], getline(1, 2))
+endfunc

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1746,
 /**/
     1745,
 /**/