cext: refactor cleanup code in bdiff()

A future commit will need to introduce additional cleanup code.

We refactor the cleanup code to check NULL before calling free().
We also initialize these variables as NULL.

We set the out of memory exception explicitly, so we can just return
result.

Differential Revision: https://phab.mercurial-scm.org/D2586

mercurial/cext/bdiff.c

@@ -62,11 +62,11 b' static PyObject *bdiff(PyObject *self, P'
 {
 	char *sa, *sb, *rb, *ia, *ib;
 	PyObject *result = NULL;
-	struct bdiff_line *al, *bl;
+	struct bdiff_line *al = NULL, *bl = NULL;
 	struct bdiff_hunk l, *h;
 	int an, bn, count;
 	Py_ssize_t len = 0, la, lb, li = 0, lcommon = 0, lmax;
-	PyThreadState *_save;
+	PyThreadState *_save = NULL;
 
 	l.next = NULL;
 
@@ -89,12 +89,16 b' static PyObject *bdiff(PyObject *self, P'
 
 	an = bdiff_splitlines(sa + lcommon, la - lcommon, &al);
 	bn = bdiff_splitlines(sb + lcommon, lb - lcommon, &bl);
-	if (!al || !bl)
-		goto nomem;
+	if (!al || !bl) {
+		PyErr_NoMemory();
+		goto cleanup;
+	}
 
 	count = bdiff_diff(al, an, bl, bn, &l);
-	if (count < 0)
-		goto nomem;
+	if (count < 0) {
+		PyErr_NoMemory();
+		goto cleanup;
+	}
 
 	/* calculate length of output */
 	la = lb = 0;
@@ -110,7 +114,7 b' static PyObject *bdiff(PyObject *self, P'
 	result = PyBytes_FromStringAndSize(NULL, len);
 
 	if (!result)
-		goto nomem;
+		goto cleanup;
 
 	/* build binary patch */
 	rb = PyBytes_AsString(result);
@@ -130,13 +134,19 b' static PyObject *bdiff(PyObject *self, P'
 		lb = h->b2;
 	}
 
-nomem:
+cleanup:
 	if (_save)
 		PyEval_RestoreThread(_save);
-	free(al);
-	free(bl);
-	bdiff_freehunks(l.next);
-	return result ? result : PyErr_NoMemory();
+	if (al) {
+		free(al);
+	}
+	if (bl) {
+		free(bl);
+	}
+	if (l.next) {
+		bdiff_freehunks(l.next);
+	}
+	return result;
 }
 
 /*