ninja win: don't expect pdb to be generated when GenerateDebugInformation: false

if comparison was incorrect for truthy values when added at
https://codereview.chromium.org/126443004/ (such as 'false').

Test addition fails before this CL.

R=thakis@chromium.org, sky@chromium.org
BUG=chromium:404872

Review URL: https://codereview.chromium.org/483133002

git-svn-id: http://gyp.googlecode.com/svn/trunk@1967 78cadc50-ecff-11dd-a971-7dbc132099af