A quick fix for bad_alloc exceptions, asking for start > stop times
At times there was a exception creeping through from the nds2 client layer, a std::bad_alloc being thrown in the C++.
This was caused by start > end times. The nds2 client will be fixed, it will raise an exception with a message that notes the start and stop times are invalid.
This is a quick patch which just makes sure that start < end for fetch requests. I do not know if this breaks any higher level assumptions that may have led to start > end.