Fix incorrect skipping in contextAttribs parsing in eglCreateContext (library_egl.js)

Fix incorrect skipping of contextAttribs array in eglCreateContext. Otherwise the loop runs twice instead of once, and value will get incorrectly assigned to param, causing glesContextVersion check in eglCreateContext to fail, and return 0x3005.
Sorry, I think I miswrote above. I think the following form be good to handle this:

    for(;;) {
        var param = {{{ makeGetValue('contextAttribs', '0', 'i32') }}};
        if (param == 0x3098 /*EGL_CONTEXT_CLIENT_VERSION*/) {
          glesContextVersion = {{{ makeGetValue('contextAttribs', '4', 'i32') }}};
        } else if (param == 0x3038 /*EGL_NONE*/) {
          break;
        } else {
          EGL.setErrorCode(0x3004 /* EGL_BAD_ATTRIBUTE */); 
          return 0;
        }
        contextAttribs += 8;
    }

What do you think?