render/gles2: check external-only flag in get_or_create_buffer()
If the external-only flag is set, then the EGLImage is only supported for use with GL_TEXTURE_EXTERNAL_OES texture targets. In particular, the EGLImage cannot be bound to a RBO.
If the external-only flag is set, then the EGLImage is only supported for use with GL_TEXTURE_EXTERNAL_OES texture targets. In particular, the EGLImage cannot be bound to a RBO.