[BUG]: getPulseGenMethod for Brian 2 doesn't properly account for the simulation time line

[jonrkarr]

getPulseGenMethod fails when a pulse occurs beyond the simulation time line (steps < int("+(del_si+dur_si)+"/defaultclock.dt)). The getPulseGenMethod should be adjusted to account for this.

org.neuroml.export/src/main/java/org/neuroml/export/brian/BrianWriter.java

Line 435 in ce18e86

" np.repeat(0, (steps - int("+(del_si+dur_si)+"/defaultclock.dt))) ) ) * "+unit+" , \n"

Replace steps - int("+(del_si+dur_si)+"/defaultclock.dt) with max(0, steps - int("+(del_si+dur_si)+"/defaultclock.dt)).