Don't fail if there's no cookies file.
Don't fail if there's no cookies file.

When there's no post-review-cookies.txt file, MozillaCookieJar.load() throws an
IOError. This change adds a bare try/except around it so it doesn't crash.

datjwu/rbtools,Khan/rbtools,beol/rbtools,reviewboard/rbtools,haosdent/rbtools,davidt/rbtools,davidt/rbtools,reviewboard/rbtools,1tush/rbtools,datjwu/rbtools,halvorlu/rbtools,beol/rbtools,reviewboard/rbtools,clach04/rbtools_0.4.1,datjwu/rbtools,haosdent/rbtools,Khan/rbtools,clach04/rbtools,beol/rbtools,clach04/old_rbtools_0.3.2,haosdent/rbtools,davidt/rbtools,halvorlu/rbtools,halvorlu/rbtools,bcelary/rbtools