I'm not sure this is ever called. I tried creating a key with an invalid public key, and did not get an error. I suggest either creating a test that shows this exception being thrown, or to remove it.

Some tests I ran:
```
> key;
{ compressed: true,
  public: null,
  private: null }
> key;
{ compressed: true,
  public: null,
  private: null }
> key.public = buffertools.fill(new Buffer(65), 0);
<Buffer 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ...>
> key;
{ compressed: true,
  public: null,
  private: null }
> key.public = buffertools.fill(new Buffer(0), 0);
<Buffer >
> key;
{ compressed: true,
  public: null,
  private: null }
> key.public = buffertools.fill(new Buffer(1), 0);
<Buffer 00>
> key;
{ compressed: true,
  public: <SlowBuffer 00>,
  private: null }
> key.public = buffertools.fill(new Buffer(33), 0);
<Buffer 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00>
> key;
{ compressed: true,
  public: <SlowBuffer 00>,
  private: null }
> key.public = buffertools.fill(new Buffer(34), 0);
<Buffer 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00>
> key;
{ compressed: true,
  public: <SlowBuffer 00>,
  private: null }
> key.public = buffertools.fill(new Buffer(35), 0);
<Buffer 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00>
> key;
{ compressed: true,
  public: <SlowBuffer 00>,
  private: null }
> key.public = buffertools.fill(new Buffer(400), 0);
<Buffer 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ...>
> key;
{ compressed: true,
  public: <SlowBuffer 00>,
  private: null }
> key.public = buffertools.fill(new Buffer(2), 0);
<Buffer 00 00>
> key;
{ compressed: true,
  public: <SlowBuffer 00>,
  private: null }
> key.public = bitcore.Key.generateSync().public;
<SlowBuffer 03 5c bc 34 88 1f da 90 09 70 ca b4 8a 2d 69 52 8b 9f b9 ca 67 54 3b 09 e5 ad 4f 74 b9 ac 0c b3 c8>
> key;
{ compressed: true,
  public: <SlowBuffer 03 5c bc 34 88 1f da 90 09 70 ca b4 8a 2d 69 52 8b 9f b9 ca 67 54 3b 09 e5 ad 4f 74 b9 ac 0c b3 c8>,
  private: null }
> key.public = buffertools.fill(new Buffer(33), 0);
<Buffer 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00>
> key;
{ compressed: true,
  public: <SlowBuffer 03 5c bc 34 88 1f da 90 09 70 ca b4 8a 2d 69 52 8b 9f b9 ca 67 54 3b 09 e5 ad 4f 74 b9 ac 0c b3 c8>,
  private: null }
```