Program unexpected panic when vec is called

[bhao-Soo]

What version of regex are you using?

1.7.1

Describe the bug at a high level.

Program index out of boud for vector, which causing a panic.

What are the steps to reproduce the behavior?

Using auto-generated fuzz target can reproduce the behavior. it was uploaded to the issue platform.
index_out_of_bound.zip

Similar problems were found in the fuzzy test:

• regex/src/re_unicode.rs:58:10
• regex/src/exec.rs:461:22
• regex/src/exec.rs:784:14
• regex/src/re_unicode.rs:58:10

What is the actual behavior?

Panic happens, the program crashes.

What is the expected behavior?

Handle index out of bound without causing a panic

[BurntSushi]

This issue is invalid in the same way that #948 is invalid. The offset provided is itself incorrect.