perf python: Decrement the refcount of just created event on failure

To avoid a leak if we have the python object but then something happens
and we need to return the operation, decrement the offset of the newly
created object.

Fixes: 377f698db1 ("perf python: Add struct evsel into struct pyrf_event")
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Reviewed-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250312203141.285263-5-acme@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

tools/perf/util/python.c

@@ -1012,6 +1012,7 @@ static PyObject *pyrf_evlist__read_on_cpu(struct pyrf_evlist *pevlist,
 
 		evsel = evlist__event2evsel(evlist, event);
 		if (!evsel) {
+			Py_DECREF(pyevent);
 			Py_INCREF(Py_None);
 			return Py_None;
 		}
@@ -1023,9 +1024,12 @@ static PyObject *pyrf_evlist__read_on_cpu(struct pyrf_evlist *pevlist,
 		/* Consume the even only after we parsed it out. */
 		perf_mmap__consume(&md->core);
 
-		if (err)
+		if (err) {
+			Py_DECREF(pyevent);
 			return PyErr_Format(PyExc_OSError,
 					    "perf: can't parse sample, err=%d", err);
+		}
+
 		return pyevent;
 	}
 end: