Validation fix for draw with primcount <= 0 A buffer size validation check was returning an invalid operation error based on buffer size, even when primcount is <= 0 (so the buffer isn't used). Fixes the following WebGL 1.0.4 test with SwANGLE: conformance/extensions/angle-instanced-arrays-out-of-bounds.html Bug: b/154628007 Change-Id: Ibfe4eb57f17cd07100fb8dfbe8069e9ec7515160 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2168546 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Alexis Hétu <sugoi@chromium.org>