Add dlerror() to DynamicLibrary::open

I had some troubles loading a dylib on osx.
So i added a dlerror() call to DynamicLibrary::open to be able to spot the issue better. Might be a good thing to add.

bool DynamicLibrary::open (const String& name)



    handle = dlopen (name.isEmpty() ? nullptr : name.toUTF8().getAddress(), RTLD_LOCAL | RTLD_NOW);

const char* error = dlerror();

if (error != nullptr)





    return handle != nullptr;



Or maybe better, a method to get the last error.  String getLastError();

Yes, good idea!

(actually what we should do is to replace the bool return type with a Result object)