nice fix

mlmc/src/basics/Sample.hpp

@@ -22,7 +22,8 @@ public:
   SampleID() {}
 
   SampleID(int level, int number, bool coarse, const std::string &name = "U") :
-    fLevel(level), cLevel(level - 1), number(number), coarse(coarse), name(name) {}
+    fLevel(level), cLevel( (level > 0) ? (level - 1) : 0),
+    number(number), coarse(coarse), name(name) {}
 
   int level() const {
     if (coarse) return cLevel;