Make LocationModel compatible with $guarded fields

[voveson]

Closes #52.

Checks if the implementing model has defined $fillable properties before adding location properties as fillable. This allows the developer to choose either the whitelist approach (eg. defining $fillable fields), or the blacklist approach (eg. defining $guarded fields) for mass-assignment protection.

[LukeTowers]

Shouldn't this check the guarded properties instead? A model could define neither but disallow mass assignment until one of them is defined, in which case we need the behavior to add those fillable properties.

[voveson]

Ah, you're right. I didn't realize that the default behavior is to guard everything. It looks like the GuardsAttributes trait defines guarded as follows:

protected $guarded = ['*'];

So you are right, if the developer does not define either $guarded or $fillable, by default everything is guarded. I will update to account for that.

[LukeTowers]

Doesn't this cause an issue if the developer has overridden the guarded property to manually blacklist guarded properties?

[voveson]

I hope not, since that's the very issue this PR is attempting to solve! 😉Are you seeing something different in your testing?

In my testing, this patch works as expected in all of the following cases:

1. Developer overrides the $guarded array
2. Developer overrides the $fillable array
3. Developer does not override $guarded or $fillable

The only case that is not supported is if the developer overrides both $fillable and $guarded. This seems acceptable to me, since the docs explicitly state:

Of course, you should use either $fillable or $guarded - not both

[voveson]

Hey @LukeTowers, I understand you're busy -- I just wanted to make sure that you're not still waiting on something from me. If any other changes are needed before this can be merged in, please let me know. Thanks!

[LukeTowers]

@voveson thanks for the reminder :)