Use `GL_NUM_EXTENSIONS` and `glGetStringi` to check OpenGL extensions

[jgcodes2020]

According to official documentation, glGetString(GL_EXTENSIONS) will return NULL. (link)

The officially supported method goes something like:

int numExtensions = 0;
glGetIntegerv(GL_NUM_EXTENSIONS, &numExtensions);
for (int i = 0; i < numExtensions; i++) {
  const char* ext = (const char*) glGetStringi(GL_EXTENSIONS, i);
  // do something with ext
}

I ran into this while integrating Mupen64Plus into my own frontend.

[richard42]

I believe that this documentation is referring to the Core (OpenGL 3.0) profile, whereas these video plugins are so old that they are still using the Compatibility (OpenGL 1.2) profile. So the current behavior is correct.