Commit 3c1e83c7 changed uses of arrays of CoglAttributes to take a
length instead of being NULL terminated. In cogl_primitive_new it was
still adding the NULL terminator to the array it passes to
cogl_primitive_new_with_attributes but then it was also including this
terminator in the count so it would just segfault when it tries to ref
the NULL pointer. Also _cogl_primitive_new_with_attributes_unref was
still trying to detect the NULL terminator so it would also crash.
