Fix wifi AP backup

An OutputStream buffers only by explicit contract.  OutputStreamWriter
buffers internally, always.  Do not get these behaviors confused.

Bug 19341967

Change-Id: I0610ed625b0175620083dd286f3a73c24956b171

packages/SettingsProvider/src/com/android/providers/settings/SettingsBackupAgent.java

@@ -942,6 +942,7 @@ public class SettingsBackupAgent extends BackupAgentHelper {
                 ByteArrayOutputStream bos = new ByteArrayOutputStream();
                 OutputStreamWriter out = new OutputStreamWriter(bos);
                 fromFile.write(out);
+                out.flush();
                 return bos.toByteArray();
             } else {
                 return EMPTY_DATA;