LinuxVNC: Fix for no input possible because of ctrl key being stuck.

Issue was reported as Debian bug ##555988,
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=555988Signed-off-by: Christian Beier <dontmind@freeshell.org>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

vncterm/LinuxVNC.c

@@ -62,6 +62,7 @@ void do_key(rfbBool down,rfbKeySym keySym,rfbClientPtr cl)
       }
     }
   } else if(keySym==XK_Control_L || keySym==XK_Control_R)
+    if(isControl>0)
       isControl--;
 }