Comment that cache-filling should be no-fail (we don't use it anyway)

src/BlockFile.h

@@ -78,7 +78,8 @@ class PROFILE_DLL_API BlockFile /* not final, abstract */ {
 
    // Fill read cache of block file, if it has any
    virtual bool GetNeedFillCache() { return false; }
-   virtual void FillCache() { /* no cache by default */ }
+
+   virtual void FillCache() /* noexcept */ { /* no cache by default */ }
 
    /// Stores a representation of this file in XML
    virtual void SaveXML(XMLWriter &xmlFile) = 0;

src/DirManager.h

@@ -177,7 +177,9 @@ class PROFILE_DLL_API DirManager final : public XMLTagHandler {
    // Write all write-cached block files to disc, if any
    void WriteCacheToDisk();
 
-   // Fill cache of blockfiles, if caching is enabled (otherwise do nothing)
+   // (Try to) fill cache of blockfiles, if caching is enabled (otherwise do
+   // nothing)
+   // A no-fail operation that does not throw
    void FillBlockfilesCache();
 
  private:

src/Project.cpp

@@ -3145,6 +3145,7 @@ void AudacityProject::OpenFile(const wxString &fileNameArg, bool addtohistory)
          mImportXMLTagHandler.reset();
 
          if ( bParseSuccess ) {
+            // This is a no-fail:
             GetDirManager()->FillBlockfilesCache();
             EnqueueODTasks();
          }
@@ -4183,6 +4184,7 @@ bool AudacityProject::Import(const wxString &fileName, WaveTrackArray* pTrackArr
                OnEffectFlags::kConfigured);
    }
 
+   // This is a no-fail:
    GetDirManager()->FillBlockfilesCache();
    return true;
 }

src/blockfile/SimpleBlockFile.cpp

@@ -267,6 +267,8 @@ bool SimpleBlockFile::WriteSimpleBlockFile(
    return true;
 }
 
+// This function should try to fill the cache, but just return without effect
+// (not throwing) if there is failure.
 void SimpleBlockFile::FillCache()
 {
    if (mCache.active)

src/blockfile/SimpleBlockFile.h

@@ -82,7 +82,8 @@ class PROFILE_DLL_API SimpleBlockFile /* not final */ : public BlockFile {
    void WriteCacheToDisk() override;
 
    bool GetNeedFillCache() override { return !mCache.active; }
-   void FillCache() override;
+
+   void FillCache() /* noexcept */ override;
 
  protected: