Fixes a seg fault caused by HepVector sigmas not being initialized in...
requested to merge mmuskinj/CLHEP:2_4_0_1_atlaspatch-fix-RandMultiGauss into CLHEP_2_4_0_1_atlaspatch
Fixes a seg fault caused by HepVector sigmas not being initialized in prepareUsigmas at line sigmas(i) = sqrt ( s2 );.
reported in CLHEP-154