automatic install resource detection code is broken

Hi,

After building belr and its tester on Guix, and having installed it this way:

$ tree /gnu/store/25wcq0p9dqxsqmj3126xfy31s8f9vv09-belr-4.4.34-tester
/gnu/store/25wcq0p9dqxsqmj3126xfy31s8f9vv09-belr-4.4.34-tester
├── bin
│   └── belr_tester
└── share
    ├── belr_tester
    │   └── res
    │       ├── basicgrammar.txt
    │       ├── register.txt
    │       ├── response.txt
    │       ├── sipgrammar.txt
    │       └── vcardgrammar.txt
    └── doc
        └── belr-4.4.34
            └── LICENSE.txt

6 directories, 7 files

I was surprised that running the belr_tester binary would fail locating its own resources.

It turns out this is caused by this code https://gitlab.linphone.org/BC/public/bctoolbox/-/blob/master/src/tester.c#L1066, which takes precedence over the (correctly resolved) installed_resources_path variable. I'm not sure under which condition it is expected that CWD or its parent would not exist; that seems an odd check to me. I've patched out these two checks locally and now it works as I would expect.