Fix misuse of PyUnicode_GET_SIZE() => PyUnicode_GET_LENGTH()

And PyUnicode_GetSize() => PyUnicode_GetLength()
diff --git a/Objects/exceptions.c b/Objects/exceptions.c
index a1b79a8..37b7875 100644
--- a/Objects/exceptions.c
+++ b/Objects/exceptions.c
@@ -1273,7 +1273,7 @@
     if (!obj)
         return -1;
     *start = ((PyUnicodeErrorObject *)exc)->start;
-    size = PyUnicode_GET_SIZE(obj);
+    size = PyUnicode_GET_LENGTH(obj);
     if (*start<0)
         *start = 0; /*XXX check for values <0*/
     if (*start>=size)
@@ -1341,7 +1341,7 @@
     if (!obj)
         return -1;
     *end = ((PyUnicodeErrorObject *)exc)->end;
-    size = PyUnicode_GET_SIZE(obj);
+    size = PyUnicode_GET_LENGTH(obj);
     if (*end<1)
         *end = 1;
     if (*end>size)