patch 9.0.0018: going over the end of the typahead

Problem:    Going over the end of the typahead.
Solution:   Put a NUL after the typeahead.
diff --git a/src/term.c b/src/term.c
index 754ef82..7d7b84b 100644
--- a/src/term.c
+++ b/src/term.c
@@ -5393,6 +5393,7 @@
 	if (*tp == ESC && !p_ek && (State & MODE_INSERT))
 	    continue;
 
+	tp[len] = NUL;
 	key_name[0] = NUL;	// no key name found yet
 	key_name[1] = NUL;	// no key name found yet
 	modifiers = 0;		// no modifiers yet