r_gnuUtilizationRate crashes if unitSize is zero
No check if unitSize is zero. It should not be, but causes a crash if input data has flaws
= r_gnuTotalGen(grid, node, unit)
/ [
+ (p_gnu(grid, node, unit, 'capacity') + r_invest(unit)*p_gnu(grid, node, unit, 'unitSize'))
* (mSettings(m, 't_end') - (mSettings(m, 't_start') + mSettings(m, 't_initializationPeriod')) + 1)
* mSettings(m, 'stepLengthInHours')
]; // END division