Allow setting -BlacklistThreshold to 0 to disable it

common/rfb/Blacklist.cxx

@@ -42,6 +42,9 @@ Blacklist::~Blacklist() {
 }
 
 bool Blacklist::isBlackmarked(const char* name) {
+  if (!threshold)
+    return false;
+
   BlacklistMap::iterator i = blm.find(name);
   if (i == blm.end()) {
     // Entry is not already black-marked.