Fix build of PostgreSQL plugin with -Werror on Windows/64bit.

Fix MSVC warning:
sql\drivers\psql\qsql_psql.cpp(452): warning C4267: 'argument': conversion from 'size_t' to 'int', possible loss of data

Change-Id: I44a902a9169efa568dcd82bdc08c5b97e661d65a
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@theqtcompany.com>

src/sql/drivers/psql/qsql_psql.cpp

@@ -449,7 +449,7 @@ QVariant QPSQLResult::data(int i)
     case QVariant::ByteArray: {
         size_t len;
         unsigned char *data = PQunescapeBytea((const unsigned char*)val, &len);
-        QByteArray ba((const char*)data, len);
+        QByteArray ba(reinterpret_cast<const char *>(data), int(len));
         qPQfreemem(data);
         return QVariant(ba);
     }