libmesh_error() instead of LIBMESH_THROW()

Not sure how we were getting away with passing 0 arguments to a macro
defined to take 1...

Author: roystgnr

src/systems/equation_systems_io.C

@@ -131,7 +131,7 @@ void EquationSystems::read (std::string_view name,
                        << "Good Luck!!\n"
                        << "*********************************************************************\n"
                        << std::endl;
-          LIBMESH_THROW();
+          libmesh_error();
         }
     }