Fix a compile warning for bdiff

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Hash: SHA1

Fix a compile warning for bdiff

manifest hash: 263a8d670a4960f57b6738d41b40626efe1d90d5
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mercurial/bdiff.c

@@ -239,7 +239,7 b' static struct hunklist diff(struct line '
 
 static PyObject *blocks(PyObject *self, PyObject *args)
 {
-	PyObject *sa, *sb, *rl, *m;
+	PyObject *sa, *sb, *rl = NULL, *m;
 	struct line *a, *b;
 	struct hunklist l;
 	struct hunk *h;