patch 9.0.1516: cannot use special keys in <Cmd> mapping

Problem:    Cannot use special keys in <Cmd> mapping.
Solution:   Do allow for special keys in <Cmd> and <ScriptCmd> mappings.
            (closes #12326)
diff --git a/src/ops.c b/src/ops.c
index 33fedba..4c64e05 100644
--- a/src/ops.c
+++ b/src/ops.c
@@ -3701,7 +3701,7 @@
 		    ResetRedobuff();
 		else
 		{
-		    AppendToRedobuffLit(repeat_cmdline, -1);
+		    AppendToRedobuffSpec(repeat_cmdline);
 		    AppendToRedobuff(NL_STR);
 		    VIM_CLEAR(repeat_cmdline);
 		}