macOS Catalina gladLoadGL error
When I try load glad

```cpp
#include <glad/glad.h>

int main() {
  if (!gladLoadGL()) {
    // do something ...
  }

  // do something ...
}
```

I see exception __'EXC_BAD_ACCESS'__ in glad.c, on line 9917

```cpp
if(glGetString(GL_VERSION) == NULL) return 0;
```

_How fix it?_

Best regards,
Roman S
