Fix latent bug in gdbpy_lookup_static_symbols

gdbpy_lookup_static_symbols is missing an error check for the case
where symbol_to_symbol_object returns NULL.

Approved-By: Tom de Vries <tdevries@suse.de>

gdb/python/py-symbol.c

@@ -632,10 +632,11 @@ gdbpy_lookup_static_symbols (PyObject *self, PyObject *args, PyObject *kw)
 
 		  if (symbol != nullptr)
 		    {
-		      PyObject *sym_obj
-			= symbol_to_symbol_object (symbol);
+		      PyObject *sym_obj = symbol_to_symbol_object (symbol);
+		      if (sym_obj == nullptr)
+			return nullptr;
 		      if (PyList_Append (return_list.get (), sym_obj) == -1)
-			return NULL;
+			return nullptr;
 		    }
 		}
 	    }