QJsonParser: fix UB (misaligned store) in Parser::parseNumber()

Found by UBSan:

  qjsonparser.cpp:741:30: runtime error: store to misaligned address 0x0000019b1e94 for type 'quint64', which requires 8 byte alignment

Fix by using the qToLittleEndian() overload that can
store to misaligned memory.

Change-Id: Ib84bd30b13c68f7fdb8870c9fbbfac15cff0112d
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/corelib/json/qjsonparser.cpp

@@ -732,7 +732,7 @@ bool Parser::parseNumber(QJsonPrivate::Value *val, int baseOffset)
     }
 
     int pos = reserveSpace(sizeof(double));
-    *(quint64 *)(data + pos) = qToLittleEndian(ui);
+    qToLittleEndian(ui, reinterpret_cast<uchar *>(data + pos));
     if (current - baseOffset >= Value::MaxSize) {
         lastError = QJsonParseError::DocumentTooLarge;
         return false;