Prevent redundant calls to removeHandler() from throwing exceptions.

Fixes issue 7552.

Change-Id: I7f284ef9c52f264dcdf282ef4b752c049422cfc9
Review-Link: https://gwt-review.googlesource.com/#/c/1640/

Review by: goktug@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@11455 8db76d5a-ed1c-0410-87a9-c151d255dfc7
2 files changed