patch 8.2.3414: fullcommand() gives wrong name with buffer-local user command

Problem:    fullcommand() gives the wrong name if there is a buffer-local user
            command. (Naohiro Ono)
Solution:   Use a separate function to get the user command name.
            (closes #8840)
diff --git a/src/usercmd.c b/src/usercmd.c
index bc0b870..e35f4a5 100644
--- a/src/usercmd.c
+++ b/src/usercmd.c
@@ -289,7 +289,7 @@
 }
 
     char_u *
-get_user_command_name(int idx)
+expand_user_command_name(int idx)
 {
     return get_user_commands(NULL, idx - (int)CMD_SIZE);
 }
@@ -316,6 +316,32 @@
 }
 
 /*
+ * Get the name of user command "idx".  "cmdidx" can be CMD_USER or
+ * CMD_USER_BUF.
+ * Returns NULL if the command is not found.
+ */
+    char_u *
+get_user_command_name(int idx, int cmdidx)
+{
+    if (cmdidx == CMD_USER && idx < ucmds.ga_len)
+	return USER_CMD(idx)->uc_name;
+    if (cmdidx == CMD_USER_BUF)
+    {
+	// In cmdwin, the alternative buffer should be used.
+	buf_T *buf =
+#ifdef FEAT_CMDWIN
+		    (cmdwin_type != 0 && get_cmdline_type() == NUL)
+							  ? prevwin->w_buffer :
+#endif
+	    curbuf;
+
+	if (idx < buf->b_ucmds.ga_len)
+	    return USER_CMD_GA(&buf->b_ucmds, idx)->uc_name;
+    }
+    return NULL;
+}
+
+/*
  * Function given to ExpandGeneric() to obtain the list of user address type
  * names.
  */