calling load on an invalid file name

``` c++
GLMmodel* 
glmReadOBJ(char* filename)
{
  GLMmodel* model;
  FILE*     file;

  /* open the file */
  file = fopen(filename, "r");
  if (!file) {
    fprintf(stderr, "glmReadOBJ() failed: can't open data file \"%s\".\n",
        filename);
    exit(1);
  }
```

throw an exception?
nah,
let's just quit the whole program!
this is so crazy! hahaha
