gles2: Avoid crash when glGetInteger64vEXT is missing
The spec says
The GetInteger64vEXT command is required only if OpenGL ES 3.0 or later is not supported.
Some GLES 3.2 implementations like the proprietary mali driver on the rk3566 based OrangePi advertise GL_EXT_disjoint_timer_query but lack glGetInteger64vEXT
Allow wlroots compositors to use the GLES2 renderer on those devices nevertheless.