Panic in freeconf/yang library when import is missing

[davidmat50]

The library calls panicked when testing a yang file which refers to a prefix, , but module import with that prfix is missing.

panic stack:

goroutine 1 [running]:
github.com/freeconf/yang/meta.findModuleAndIsExternal({0x101a170?, 0xc0001baa90?}, {0xc0004b60fc, 0x3})
        C:/Users/dama0416/go/pkg/mod/github.com/freeconf/yang@v0.0.0-20230710114243-bc7f6c1082ad/meta/util.go:73 +0xb4
github.com/freeconf/yang/meta.(*resolver).findGrouping(0x1f737f7f3f0?, 0xc0001baa90)
        C:/Users/dama0416/go/pkg/mod/github.com/freeconf/yang@v0.0.0-20230710114243-bc7f6c1082ad/meta/resolver.go:532 +0x74
github.com/freeconf/yang/meta.(*resolver).addDataDef(0xc000099a60, {0x101b1d0, 0xc00021f320}, {0x101a170?, 0xc0001baa90?})
        C:/Users/dama0416/go/pkg/mod/github.com/freeconf/yang@v0.0.0-20230710114243-bc7f6c1082ad/meta/resolver.go:414 +0xd2
github.com/freeconf/yang/meta.(*resolver).dataDef(0xc00021f320?, {0x101b1d0, 0xc00021f320}, {0xc00051b400?, 0x2, 0xe01f?})
        C:/Users/dama0416/go/pkg/mod/github.com/freeconf/yang@v0.0.0-20230710114243-bc7f6c1082ad/meta/resolver.go:371 +0xaa
github.com/freeconf/yang/meta.(*resolver).addDataDef(0xc000099a60, {0x101b240, 0xc000002f00}, {0x1019fb0?, 0xc00021f320?})
        C:/Users/dama0416/go/pkg/mod/github.com/freeconf/yang@v0.0.0-20230710114243-bc7f6c1082ad/meta/resolver.go:478 +0x429
github.com/freeconf/yang/meta.(*resolver).dataDef(0xc000204780?, {0x101b240, 0xc000002f00}, {0xc000516770?, 0x1, 0xcd0dc7?})
        C:/Users/dama0416/go/pkg/mod/github.com/freeconf/yang@v0.0.0-20230710114243-bc7f6c1082ad/meta/resolver.go:371 +0xaa
github.com/freeconf/yang/meta.(*resolver).module(0xc00000a358?, 0xc000002f00)
        C:/Users/dama0416/go/pkg/mod/github.com/freeconf/yang@v0.0.0-20230710114243-bc7f6c1082ad/meta/resolver.go:93 +0x233
github.com/freeconf/yang/meta.resolve(0x10?)
        C:/Users/dama0416/go/pkg/mod/github.com/freeconf/yang@v0.0.0-20230710114243-bc7f6c1082ad/meta/resolver.go:25 +0x6a
github.com/freeconf/yang/meta.Compile(0xc000002f00)
        C:/Users/dama0416/go/pkg/mod/github.com/freeconf/yang@v0.0.0-20230710114243-bc7f6c1082ad/meta/compile.go:18 +0x2c
github.com/freeconf/yang/parser.LoadModuleWithOptions(0xc00051b380, {0xc00001e0e0, 0xa}, {{0x0?, 0x0?}, {0x0?, 0xc000099c60?}})
        C:/Users/dama0416/go/pkg/mod/github.com/freeconf/yang@v0.0.0-20230710114243-bc7f6c1082ad/parser/loader.go:72 +0x1fd
github.com/freeconf/yang/parser.LoadModule(...)
        C:/Users/dama0416/go/pkg/mod/github.com/freeconf/yang@v0.0.0-20230710114243-bc7f6c1082ad/parser/loader.go:16
        .
        .
        .

File used:

module panic-case {
    yang-version "1.1";
    namespace "urn:params:panic-case";
    prefix panic-case;

    /*import module_for_import {
        prefix imp;
    }*/

    container customer {
        leaf simple-leaf {
            type string;
        }
        uses imp:grouping-test;
    }
}

[dhubler]

fixed