Extend the info log length checks to shader_utils used by tests, and
treat info log with length 1 as empty, since it can only include the
null terminator. At least the Intel GL driver may generate "\0" as
info log in some situations, for example when compiling a user-defined
function with 50000 parameters.

BUG=angleproject:1323

Change-Id: I00f2965539ec235cb949c80c2a9e1d063d32fa15
Reviewed-on: https://chromium-review.googlesource.com/331461Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>