QFile::decodeName unnecessarily allocates memory

QString QFile::decodeName(const char *localFileName) creates QByteArray from the passed const char * argument in order to finally call QString::fromLocal8Bit(const QByteArray &str).

QByteArray constructor makes a deep copy of the const char * argument, which can be avoided if QFile::decodeName called QString::fromLocal8Bit(const char *str, int size = -1) instead.

This is a trivial fix which will save memory allocations and improve performance. I attach a patch for this.