Fix a race condition where we might get updates thrown at us right after a
framebuffer switch, but before we've been given the pointer to the new
framebuffer.


git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4839 3789f03b-4d11-0410-bbf8-ca57d06f2519
6 files changed