[Bugfix] Handle situation when viewer doesn't send the key release event well.

Happens for example with TightVNC 1.3.10 viewer during following sequence:
"press shift" + "press a" + "release shift" + "release a"


git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4237 3789f03b-4d11-0410-bbf8-ca57d06f2519
1 file changed