Fixes "out-of-line definition" error in CLANG

```
> libspotify@0.0.1 install /Users/tim/Code/test/spotinfringe/lib/node-libspotify
> node-gyp configure build




  CXX(target) Release/obj.target/libspotify/src/album.o
In file included from ../src/album.cc:20:
../src/common.h:210:47: error: default arguments cannot be added to an out-of-line definition of a member
      of a class template
    ObjectHandle<T>::ObjectHandle(const char* name = NULL) : pointer(NULL) {
                                              ^      ~~~~
1 error generated.
make: *** [Release/obj.target/libspotify/src/album.o] Error 1
```