ValidateDrawElements: check count > 0 then compute the index range Otherwise glDrawElements(GL_TRIANGLES, -1, nullptr) would crash. This was found by an ASSERT in ComputeIndexRange triggered by dEQP-GLES2.functional.negative_api.vertex_array.draw_elements BUG= Change-Id: I5269031fa35aa6403c844561e04158361ee7950f Reviewed-on: https://chromium-review.googlesource.com/292710 Tested-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>