The ternary operator determines that the common type is the value type, causing
a copy of PixelUnpackState.  If PixelUnpackState::pixelBuffer is non-null then
there is an assertion failure in the destructor on any call to Texture::setImage.

See:http://stackoverflow.com/a/30088030

BUG=angleproject:1149

Change-Id: I9654e65956339d6b6966ad65a98cf37ad4e00452
Reviewed-on: https://chromium-review.googlesource.com/297084Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>