Auto merge of #4486 - lzutao:fix-panic-unseparate-literals, r=flip1995
Auto merge of #4486 - lzutao:fix-panic-unseparate-literals, r=flip1995

Fix index out of bound in case of empty snippet

cc #4480

changelog: none

graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust