Fixed a bug with a crash if the link with the data cannot be opened

include/layereddata.h

@@ -49,14 +49,15 @@ class LayeredData: public NCFuncs
   }
 
   const NCFileA* operator->() const { return &nc; }
-  explicit operator bool() const { return nc; }
-  MDateTime Begin() const { return times.front(); }
-  MDateTime End() const { return times.back(); }
+  explicit       operator bool() const { return nc; }
+  MDateTime      Begin() const { return times.front(); }
+  MDateTime      End() const { return times.back(); }
 
   const NCFileA& Get() const { return nc; }
 
   const std::vector<MDateTime>& Times() const { return times; }
-  size_t                        Index(MDateTime tm) const
+
+  size_t Index(MDateTime tm) const
   {
    if(tm < Begin() || tm > End()) return 0;
    size_t b = 0, e = times.size() - 1;
@@ -73,6 +74,8 @@ class LayeredData: public NCFuncs
    }
    return 0;
   }
+
+  const MString& Url() const { return url; }
  };
  std::vector<NC>        nc;
  std::vector<real>      depths;

src/layereddata.cpp

@@ -51,8 +51,9 @@ MString LayeredData::Open(const MString& dataset)
    nc.emplace_back(std::move(url));
    if(!nc.back())
    {
+    auto failedurl = nc.back().Url();
     nc.clear();
-    return "Can't connect to url " + url;
+    return "Can't connect to url " + failedurl;
    }
   }
   else