Thanks for reporting your issue. Please make sure these boxes are checked before submitting your issue - thank you!

- [X] I looked for a similar issue and couldn't find any.
- [X] I tried with the latest version of GPAC. Installers available at http://gpac.io/downloads/gpac-nightly-builds/
- [X] I give enough information for contributors to reproduce my issue: https://github.com/jadarve/gpac_experiments/blob/main/code_experiments/create_session.c

When using the C-api, there is a small inconsistency in the `gf_fs_load_filter` when passing an empty string as filter name.

```c
#include <stdio.h>
#include <gpac/filters.h>

int main(int argc, const char** argv) {

    GF_FilterSession *session = gf_fs_new_defaults(0u);
    if (session == NULL)
    {
        fprintf(stderr, "Failed to create GPAC session\n");
        return EXIT_FAILURE;
    }

    GF_Err gf_err = GF_OK;
    GF_Filter *filter_ptr = gf_fs_load_filter(session, "", &gf_err);

    const char* err_str = gf_error_to_string(gf_err);
    printf("Error code %d: %s\n", gf_err, err_str);


    if (filter_ptr == NULL) {
        printf("Filter ptr NULL\n");
    } else {
        printf("Filter loaded\n");
    }

    return EXIT_SUCCESS;
}
```

The code above prints:

``` 
Error code 0: No Error
Filter ptr NULL
```

With an extra log line `Missing filter name in` produced by gpac logs.

Instead, if I run the code above with `GF_Filter *filter_ptr = gf_fs_load_filter(session, "some_unknown_filter", &gf_err);`, the output is:

```
Error code -11: Filter not found for the desired type
Filter ptr NULL
```
Inconsistent error code on gf_fs_load_filter()
This is a GitHub Issue
repo:gpac
owner:gpac
Title : Inconsistent error code on gf_fs_load_filter()
Issue date:

--- start body ---
Thanks for reporting your issue. Please make sure these boxes are checked before submitting your issue - thank you!

- [X] I looked for a similar issue and couldn't find any.
- [X] I tried with the latest version of GPAC. Installers available at http://gpac.io/downloads/gpac-nightly-builds/
- [X] I give enough information for contributors to reproduce my issue: https://github.com/jadarve/gpac_experiments/blob/main/code_experiments/create_session.c

When using the C-api, there is a small inconsistency in the `gf_fs_load_filter` when passing an empty string as filter name.

```c
#include <stdio.h>
#include <gpac/filters.h>

int main(int argc, const char** argv) {

    GF_FilterSession *session = gf_fs_new_defaults(0u);
    if (session == NULL)
    {
        fprintf(stderr, "Failed to create GPAC session\n");
        return EXIT_FAILURE;
    }

    GF_Err gf_err = GF_OK;
    GF_Filter *filter_ptr = gf_fs_load_filter(session, "", &gf_err);

    const char* err_str = gf_error_to_string(gf_err);
    printf("Error code %d: %s\n", gf_err, err_str);


    if (filter_ptr == NULL) {
        printf("Filter ptr NULL\n");
    } else {
        printf("Filter loaded\n");
    }

    return EXIT_SUCCESS;
}
```

The code above prints:

``` 
Error code 0: No Error
Filter ptr NULL
```

With an extra log line `Missing filter name in` produced by gpac logs.

Instead, if I run the code above with `GF_Filter *filter_ptr = gf_fs_load_filter(session, "some_unknown_filter", &gf_err);`, the output is:

```
Error code -11: Filter not found for the desired type
Filter ptr NULL
```
--- end body ---
