Fix crash in QDBusDemarshaller QStringList extraction

Fix crash in QDBusDemarshaller QStringList extraction

QDBusArgument QStringList extraction operator and QDBusDemarshaller that
implements the extraction do not check the type of the extracted value.
When extracting a QStringList and the value actually is e.g. an array of
bytes the string list extraction will crash as it interprets the bytes as
char pointers.

The fix adds DBus type checks to QDBusArgument QStringList extraction
operator implementations.
The checks are as permissive as possible provided crashes are avoided.

Task-number: QTBUG-22840
Change-Id: I4b67d75b59c5052d939f3a69f3e92dabdb3bdd6b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>