Commit autosave blobs during recording only as needed...

... when there really is at least one new sample block committed to the table,
which is typically only once in about every six seconds, with the default rate
and sample format.

Also renamed a callback function more aptly, since blocks are not files any
more.

src/WaveClip.cpp

@@ -1202,13 +1202,14 @@ void WaveClip::GetDisplayRect(wxRect* r)
    *r = mDisplayRect;
 }
 
-void WaveClip::Append(samplePtr buffer, sampleFormat format,
+bool WaveClip::Append(samplePtr buffer, sampleFormat format,
                       size_t len, unsigned int stride /* = 1 */)
 // PARTIAL-GUARANTEE in case of exceptions:
 // Some prefix (maybe none) of the buffer is appended, and no content already
 // flushed to disk is lost.
 {
    //wxLogDebug(wxT("Append: len=%lli"), (long long) len);
+   bool result = false;
 
    auto maxBlockSize = mSequence->GetMaxBlockSize();
    auto blockSize = mSequence->GetIdealAppendLen();
@@ -1228,6 +1229,7 @@ void WaveClip::Append(samplePtr buffer, sampleFormat format,
          // flush some previously appended contents
          // use STRONG-GUARANTEE
          mSequence->Append(mAppendBuffer.ptr(), seqFormat, blockSize);
+         result = true;
 
          // use NOFAIL-GUARANTEE for rest of this "if"
          memmove(mAppendBuffer.ptr(),
@@ -1255,6 +1257,8 @@ void WaveClip::Append(samplePtr buffer, sampleFormat format,
       buffer += toCopy * SAMPLE_SIZE(format) * stride;
       len -= toCopy;
    }
+
+   return result;
 }
 
 void WaveClip::Flush()