Bug to take into accoung modified user Fortran for flowrate or tracers with punctual sources + SOURCES FILE

G_G_H pointed a bug when trying to apply user Fortran for tracers with punctual sources + using SOURCES FILE with TELEMAC-3D (user_t3d_trsce.f), see http://opentelemac.org/index.php/kunena/21-telemac-3d/14763-subroutine-user-t3d-trsce-f