PPAPI: Fix extra whitespace nit in plugin_main_nacl.cc

bbudge pointed this out in https://codereview.chromium.org/26854003 and I forgot to fix it.

BUG=305903
TBR=bbudge@chromium.org

Review URL: https://codereview.chromium.org/26997008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228824 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228824