Bug 477934 nsSafeFileOutputStream (prefs.js) not safe from system crashes

r=biesi

netwerk/base/src/nsFileStreams.cpp

@@ -531,6 +531,7 @@ nsSafeFileOutputStream::Close()
 NS_IMETHODIMP
 nsSafeFileOutputStream::Finish()
 {
+    Flush();
     nsresult rv = nsFileOutputStream::Close();
 
     // if there is no temp file, don't try to move it over the original target.