Compiling an assert in Program.cpp was failing at least on GCC 4.8
because it compared unsigned size_t to zero, a comparison that was always
true. The C standard defines size_t as unsigned, so the assert shouldn't
be necessary on other platforms either.

There was already a commit on top of the patch that added the bug, so it
is simpler to fix the problem by changing the assert rather than
reverting.

TEST=standalone debug build on Linux

Change-Id: Ifd910332a770f7360a15c31706beca740d0f289d
Reviewed-on: https://chromium-review.googlesource.com/294971Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>