Small issue that isn't really relevant because there should always exist at...

Small issue that isn't really relevant because there should always exist at least one element. However it shouldn't crash when there isn't a single element.

src/Algorithms/IndexMap.cpp

@@ -265,7 +265,8 @@ void IndexMap::saveSDDS(double initialPathLength) const {
     }
 
     // add row if range of first sector starts after initialPathLength
-    if (std::get<0>(sectors[0]) > initialPathLength) {
+    if (sectors.size() > 0 &&
+        std::get<0>(sectors[0]) > initialPathLength) {
         auto tmp = sectors;
         sectors = std::vector<std::tuple<double, std::vector<double>, std::string> >(1);
         std::get<0>(sectors[0]) = initialPathLength;