fix index out of range when quickly typing and or changing suggestions

completion.go

@@ -47,6 +47,8 @@ func (c *CompletionManager) GetSelectedSuggestion() (s Suggest, ok bool) {
 		debug.Assert(false, "must not reach here")
 		c.selected = -1
 		return Suggest{}, false
+	} else if c.selected >= len(c.tmp) {
+		return Suggest{}, false
 	}
 	return c.tmp[c.selected], true
 }