Fix error message when using "gcl try nonexistentcl".

Call ChangeInfo.Load() with fail_on_not_found=True to get a good error message in this case.

BUG=none
TEST=manual

Review URL: http://codereview.chromium.org/8692007

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@112018 0039d316-1c4b-4281-b951-d872f2087c98

gcl.py

@@ -1309,7 +1309,7 @@ def CMDtry(args):
                                                 True, True)
   else:
     change_info = ChangeInfo.Load(args[0], GetRepositoryRoot(),
-                                  False, True)
+                                  True, True)
   if change_info.GetFiles():
     args = args[1:]
   else: