[Bug] When filling the template, an exception is reported when the placeholder content is '{foo\}'

### Search before asking

- [x] I searched in the [issues](https://github.com/fast-excel/fastexcel/issues) and found nothing similar.

### Fastexcel version

1.2.0

### JDK version

1.8

### Operating system

_No response_

### Minimal reproduce step

When filling the template, set the cell content to '{foo\}'

### What did you expect to see?

It will not report an error and can correctly identify the escape character

### What did you see instead?

An array index out-of-bounds exception occurred

### Anything else?

_No response_

### Are you willing to submit a PR?

- [x] I'm willing to submit a PR!