Bug 1270310 - Part 2: Pass buffer length to Assign call in ConvertStringLineBreaks. r=froydnj

The length of the new buffer being assigned in ConvertStringLineBreaks has
already been calculated, so we can pass that in.

xpcom/io/nsLinebreakConverter.cpp

@@ -478,7 +478,7 @@ nsLinebreakConverter::ConvertStringLineBreaks(nsString& aIoString,
   }
 
   if (stringBuf != aIoString.get()) {
-    aIoString.Adopt(stringBuf);
+    aIoString.Adopt(stringBuf, newLen - 1);
   }
 
   return NS_OK;