We don't generally test for the default return values of function
calls that have validation errors, but the auto-gen script might
not have been returning things correctly. For GLint values, default to
returning -1 instead of zero.

BUG=angleproject:1309

Change-Id: I736b5a7ef9b50ca1509087fe933c4a4e526531d8
Reviewed-on: https://chromium-review.googlesource.com/636522Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>