patch 8.2.2851: using <Cmd> mapping on the command line triggers CmdlineChanged

Problem:    Using <Cmd> mapping on the command line triggers CmdlineChanged.
            (Naohiro Ono)
Solution:   Jump to cmdline_not_changed if the command line didn't change.
            (closes #8208)
diff --git a/src/ex_getln.c b/src/ex_getln.c
index a9f33e6..e87b208 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -1757,9 +1757,17 @@
 	    c = safe_vgetc();
 	} while (c == K_IGNORE || c == K_NOP);
 
-	if (c == K_COMMAND
-		   && do_cmdline(NULL, getcmdkeycmd, NULL, DOCMD_NOWAIT) == OK)
-	    goto cmdline_changed;
+	if (c == K_COMMAND)
+	{
+	    int	    clen = ccline.cmdlen;
+
+	    if (do_cmdline(NULL, getcmdkeycmd, NULL, DOCMD_NOWAIT) == OK)
+	    {
+		if (clen == ccline.cmdlen)
+		    goto cmdline_not_changed;
+		goto cmdline_changed;
+	    }
+	}
 
 	if (KeyTyped)
 	{