If a write is going to go past the end of the restricted area, write up to the end before throwing an exception.

[SVN r58225]

libs/iostreams

@@ -1 +1 @@
-Subproject commit ee8183446f9e810ae57fd8f04162b9f177219655
+Subproject commit def77cf80f0354acee211c9873d350aa3024cc59