Cannot match end-of-pattern match

Hi and thanks for an amazing library - I'm developing a Fortran port of it [here](https://github.com/perazz/fortran-regex).

I've just found an issue/potential bug with the end-pattern command.

text = "table football"
pattern = "l$"

returns index=13, matchlength=3

Here's the sample test program:

```c
#include
#include
#include "re.h"
int main() {

const char *text = "table football";
const char *pattern = "l$";
int index,len;

index = re_match(pattern, text, &len);

printf("index=%d len=%d \n",index,len);
}
```

Tested on Mac with clang 13.1.6

Start with the re_match entry point declared in re.h and reproduce the sample program using pattern "l$" and text "table football". Trace the end-pattern handling and add or update a regression test so the sample returns the correct match index and length.

Written by the indexing model from the issue text.