Fix potential string over-read in mythraopconnection.

Recent changes to Qt6 or the compiler have produced new compiler
warnings.  In this case the compiler thinks it is trying to copy six
bytes from an empty QByteArray.  Add a length check to ensure that the
are enough bytes in the copy source.

mythtv/libs/libmythtv/AirPlay/mythraopconnection.cpp

@@ -1081,8 +1081,17 @@ void MythRAOPConnection::ProcessRequest(const QStringList &header,
                 i += 16;
             }
         }
-        memcpy(&from[i], m_hardwareId.constData(), AIRPLAY_HARDWARE_ID_SIZE);
-        i += AIRPLAY_HARDWARE_ID_SIZE;
+        if (m_hardwareId.size() == AIRPLAY_HARDWARE_ID_SIZE)
+        {
+            memcpy(&from[i], m_hardwareId.constData(), AIRPLAY_HARDWARE_ID_SIZE);
+            i += AIRPLAY_HARDWARE_ID_SIZE;
+        }
+        else
+        {
+            LOG(VB_PLAYBACK, LOG_ERR, LOC +
+                QString("Hardware MAC address size %1, expected %2")
+                .arg(m_hardwareId.size()).arg(AIRPLAY_HARDWARE_ID_SIZE));
+        }
 
         int pad = 32 - i;
         if (pad > 0)