Fix of a bug in Stream.cpp

Stream::find(char *target) passes NULL as “terminator” to Stream::findUntil(char *target, char *terminator), which immediately dereferences it by passing it on to strlen():
 
bool Stream::find(char *target)
{
  return findUntil(target, NULL);
}
 
// as find but search ends if the terminator string is found
bool Stream::findUntil(char *target, char *terminator)
{
  return findUntil(target, strlen(target), terminator, strlen(terminator));
}