bug fixed in nasal_vec::print and nasal_hash::print

if vec's or hash's size is 0, a bug will occur because ++depth. now the ++depth has been put behind the size()

nasal_err.h

@@ -20,7 +20,7 @@ public:
         std::ifstream fin(f,std::ios::binary);
         if(fin.fail())
         {
-            std::cout<<"[src] cannot open file <"<<f<<">\n";
+            std::cerr<<"[src] cannot open file <"<<f<<">\n";
             std::exit(1);
         }
         std::string line;