UGGrid creation with boundary segments segfaults

In some situations, UG grid segfaults during grid creation when boundary segments have been specified. A simple test code that reads a grid created by triangle is attached (together with the grid files triggering the segfault, the output, and a brief stack trace).

ugboundarysegmentstest.cpp output.txt ugboundarysegmentstest.1.node ugboundarysegmentstest.1.ele ugboundarysegmentstest.1.edge