Flush .aup before writing .au; no redundant out-of-space messages

src/xml/XMLWriter.cpp

@@ -313,14 +313,25 @@ XMLFileWriter::~XMLFileWriter()
 
 void XMLFileWriter::Commit()
 // may throw
+{
+   PreCommit();
+   PostCommit();
+}
+
+void XMLFileWriter::PreCommit()
+// may throw
 {
    while (mTagstack.GetCount()) {
       EndTag(mTagstack[0]);
    }
 
-   auto tempPath = GetName();
    CloseWithoutEndingTags();
+}
 
+void XMLFileWriter::PostCommit()
+// may throw
+{
+   auto tempPath = GetName();
    if (mKeepBackup) {
       if (! mBackupFile.Close() ||
           ! wxRenameFile( mOutputPath, mBackupName ) )

src/xml/XMLWriter.h

@@ -86,8 +86,16 @@ class AUDACITY_DLL_API XMLFileWriter final : private wxFFile, public XMLWriter {
    /// Close all tags and then close the file.
    /// Might throw.  If not, then create
    /// or modify the file at the output path.
+   /// Composed of two steps, PreCommit() and PostCommit()
    void Commit();
 
+   /// Does the part of Commit that might fail because of exhaustion of space
+   void PreCommit();
+
+   /// Does other parts of Commit that are not likely to fail for exhaustion
+   /// of space, but might for other reasons
+   void PostCommit();
+
    /// Write to file. Might throw.
    void Write(const wxString &data) override;