Clean up some dead code and MSVC warnings.

- Dead code from experiments in SelectionBar removed.
- Many warnings about unused parameters fixed with WXUNUSED()
- Many warnings about signed / unsigned comparisons cleaned up.
- Several 'local variable declared but not used' warnings fixed.

src/import/ImportFFmpeg.cpp

@@ -740,10 +740,10 @@ ProgressResult FFmpegImportFileHandle::WriteData(streamContext *sc)
    // Separate the channels and convert input sample format to 16-bit
    uint8_t *in = sc->m_decodedAudioSamples.get();
    int index = 0;
-   int pos = 0;
+   unsigned int pos = 0;
    while (pos < insamples)
    {
-      for (int chn = 0; chn < sc->m_stream->codec->channels; chn++)
+      for (size_t chn = 0; chn < (size_t)sc->m_stream->codec->channels; chn++)
       {
          if (chn < nChannels)
          {
@@ -788,7 +788,7 @@ ProgressResult FFmpegImportFileHandle::WriteData(streamContext *sc)
 
    // Write audio into WaveTracks
    auto iter2 = iter->begin();
-   for (int chn=0; chn < nChannels; ++iter2, ++chn)
+   for (size_t chn=0; chn < nChannels; ++iter2, ++chn)
    {
       iter2->get()->Append((samplePtr)tmp[chn].get(), sc->m_osamplefmt, index);
    }

src/import/ImportPCM.cpp

@@ -478,7 +478,7 @@ ProgressResult PCMImportFileHandle::Import(TrackFactory *trackFactory,
          else
             block = SFCall<sf_count_t>(sf_readf_float, mFile.get(), (float *)srcbuffer.ptr(), block);
 
-         if(block < 0 || block > maxBlock) {
+         if(block < 0 || block > (long)maxBlock) {
             wxASSERT(false);
             block = maxBlock;
          }

src/import/RawAudioGuess.cpp

@@ -15,6 +15,7 @@
 
 #include "../Audacity.h"
 #include "RawAudioGuess.h"
+#include "../AudacityException.h"
 #include "../MemoryX.h"
 
 #include <stdio.h>
@@ -187,7 +188,7 @@ static void Extract(bool bits16,
                     bool stereo,
                     bool bigendian,
                     bool offset,
-                    char *rawData, int dataSize,
+                    char *rawData, int dataSizeIn,
                     float *data1, float *data2, size_t *len1, size_t *len2)
 {
    size_t rawCount = 0;
@@ -201,14 +202,19 @@ static void Extract(bool bits16,
       /* Special case so as to not flip stereo channels during analysis */
       if (stereo && !bigendian) {
          rawData += 3;
-         dataSize -= 3;
+         dataSizeIn -= 3;
       }
       else {
          rawData++;
-         dataSize--;
+         dataSizeIn--;
       }
    }
 
+   if( dataSizeIn < 1 )
+      throw SimpleMessageBoxException{_("Bad data size")};
+
+   size_t dataSize = (size_t)dataSizeIn;
+
    if (bits16) {
       if (sign && bigendian)
          while (rawCount + 1 < dataSize) {
@@ -322,7 +328,7 @@ static int GuessFloatFormats(unsigned numTests, const ArrayOf<char> rawData[], s
     * floats with a 1-byte offset.
     */
 
-   for(int prec = 0; prec < 2; prec++) {
+   for(unsigned int prec = 0; prec < 2; prec++) {
       for(int endian = 0; endian < 2; endian++) {
          for(size_t offset = 0; offset < (4 * prec + 4); offset++) {
             unsigned finiteVotes = 0;