Manually encode '+' character, even in Qt5

From qurlquery.cpp:
// The RFC says these are the delimiters:
//    gen-delims    = ":" / "/" / "?" / "#" / "[" / "]" / "@"
//    sub-delims    = "!" / "$" / "&" / "'" / "(" / ")"
//                  / "*" / "+" / "," / ";" / "="
// [...]
// The "+" sub-delimiter is always left untouched. We never encode "+" to "%2B"
// nor do we decode "%2B" to "+", no matter what the user asks.

No rational is given for this decision. No QUrlQuery::ActuallyReallyFullyEncodedThisTime. Just broken behavior.