Perf: Fix possible memory leaks in Python interface

The function PyObject_CallObject() returns a new PyObject reference 
on which Py_DECREF has to be called to avoid memory leaks.
This patch adds these calls where necessary.

Signed-off-by: Joseph Schuchart <joseph.schuchart@tu-dresden.de>

diff --git a/tools/perf/util/scripting-engines/trace-event-python.c b/tools/perf/util/scripting-engines/trace-event-python.c
index cd9774d..ee17f64 100644
--- a/tools/perf/util/scripting-engines/trace-event-python.c
+++ b/tools/perf/util/scripting-engines/trace-event-python.c
@@ -97,6 +97,8 @@ static void define_value(enum print_arg_type field_type,
 		retval = PyObject_CallObject(handler, t);
 		if (retval == NULL)
 			handler_call_die(handler_name);
+		else
+			Py_DECREF(retval);
 	}
 
 	Py_DECREF(t);
@@ -143,6 +145,8 @@ static void define_field(enum print_arg_type field_type,
 		retval = PyObject_CallObject(handler, t);
 		if (retval == NULL)
 			handler_call_die(handler_name);
+		else
+			Py_DECREF(retval);
 	}
 
 	Py_DECREF(t);
@@ -333,6 +337,8 @@ static void python_process_tracepoint(struct perf_sample *sample,
 		retval = PyObject_CallObject(handler, t);
 		if (retval == NULL)
 			handler_call_die(handler_name);
+		else
+			Py_DECREF(retval);
 	} else {
 		handler = PyDict_GetItemString(main_dict, "trace_unhandled");
 		if (handler && PyCallable_Check(handler)) {
@@ -340,6 +346,8 @@ static void python_process_tracepoint(struct perf_sample *sample,
 			retval = PyObject_CallObject(handler, t);
 			if (retval == NULL)
 				handler_call_die("trace_unhandled");
+			else
+				Py_DECREF(retval);
 		}
 		Py_DECREF(dict);
 	}
@@ -399,6 +407,8 @@ static void python_process_general_event(struct perf_sample *sample,
 	retval = PyObject_CallObject(handler, t);
 	if (retval == NULL)
 		handler_call_die(handler_name);
+	else
+		Py_DECREF(retval);
 exit:
 	Py_DECREF(dict);
 	Py_DECREF(t);
@@ -444,8 +454,8 @@ static int run_start_sub(void)
 	retval = PyObject_CallObject(handler, NULL);
 	if (retval == NULL)
 		handler_call_die("trace_begin");
-
-	Py_DECREF(retval);
+	else
+		Py_DECREF(retval);
 	return err;
 error:
 	Py_XDECREF(main_dict);