clear vector thats supposed to receive the input field before filling it

[[Imported from SVN: r1589]]

io/file/amiramesh/amirameshreader.cc

@@ -15,6 +15,8 @@ void Dune::AmiraMeshReader<GridType>::readFunction(DiscFuncType& f, const std::s
   float* am_values_float = NULL;
   int i, j;
 
+  f = 0;
+
   // We allow fields defined on the whole grid and fields defined
   // only on the boundary.  We now check the file and proceed accordingly
   if (!am->findData("Nodes", HxFLOAT, 3, "Data") &&