Fix bug that invalid range error when requesting range starting 0

Since the change b782a56b, we use endOffsetOverride_ as the return
value of getEndByte(). But aria2 does not send Range header field when
range starts 0 (this is because some server returns error if it
received Range: 0-), and the HttpRequest::isRangeSatisfied() checks
the equality of getEndByte() and the end byte in response header and
fails. The fix is send Range header if getEndByte() is set.

src/HttpRequest.cc

@@ -199,7 +199,8 @@ std::string HttpRequest::createRequest()
     builtinHds.push_back(std::make_pair("Connection:", "close"));
   }
   if(segment_ && segment_->getLength() > 0 &&
-     (request_->isPipeliningEnabled() || getStartByte() > 0)) {
+     (request_->isPipeliningEnabled() || getStartByte() > 0 ||
+      getEndByte() > 0)) {
     std::string rangeHeader(fmt("bytes=%" PRId64 "-", getStartByte()));
     if(request_->isPipeliningEnabled()) {
       rangeHeader += util::itos(getEndByte());