Fix Python BOM script bug when output file cannot be opened. (fixes:lp:1391904)

scripts/bom-in-python/bom_csv_grouped_by_value.py

@@ -26,8 +26,9 @@ net = kicad_netlist_reader.netlist(sys.argv[1])
 try:
     f = open(sys.argv[2], 'w')
 except IOError:
+    e = "Can't open output file for writing: " + sys.argv[2]
     print(__file__, ":", e, file=sys.stderr)
-    f = stdout
+    f = sys.stdout
 
 # subset the components to those wanted in the BOM, controlled
 # by <configure> block in kicad_netlist_reader.py