Add error check comments.

These are places where we don't properly handle error returns.

src/import/ImportFLAC.cpp

@@ -304,6 +304,8 @@ std::unique_ptr<ImportFileHandle> FLACImportPlugin::Open(const wxString &filenam
       return nullptr; // File not found
    }
 
+   // FIXME: TRAP_ERR wxFILE ops in FLAC Import could fail.
+   // Seek() return value is not examined, for example.
 #ifdef USE_LIBID3TAG
    // Skip any ID3 tags that might be present
    id3_byte_t query[ID3_TAG_QUERYSIZE];

src/import/MultiFormatReader.cpp

@@ -106,6 +106,7 @@ size_t MultiFormatReader::Read(void* buffer, size_t size, size_t len, size_t str
       for (size_t n = 0; n < len; n++)
       {
          actRead += fread(&(pWork[n*size]), size, 1, mpFid);
+         // FIXME: TRAP_ERR fseek return in MultiFormatReader unchecked.
          fseek(mpFid, (stride - 1) * size, SEEK_CUR);
       }
    }

src/import/RawAudioGuess.cpp

@@ -1066,8 +1066,10 @@ int RawAudioGuess(const wxString &in_fname,
    *out_channels = 1;
 
    wxFFile in_wxFFile(in_fname, wxT("rb"));
+
+   // JKC FALSE changed to -1.
    if (!in_wxFFile.IsOpened())
-      return false;
+      return -1;
    inf = in_wxFFile.fp();
 
    if (!inf) {
@@ -1079,6 +1081,7 @@ int RawAudioGuess(const wxString &in_fname,
       return -1;
    }
 
+   // FIXME: TRAP_ERR fseek return in RawAudioGuess unchecked.
    fseek(inf, 0, SEEK_END);
    fileLen = ftell(inf);
 
@@ -1100,6 +1103,7 @@ int RawAudioGuess(const wxString &in_fname,
       /* Make it a multiple of 16 (stereo double-precision) */
       startPoint = (startPoint/16)*16;
 
+      // FIXME: TRAP_ERR fseek return in MultiFormatReader unchecked.
       fseek(inf, headerSkipSize + startPoint, SEEK_SET);
       read_data = fread(rawData[test], 1, dataSize, inf);
       if (read_data != dataSize && ferror(inf)) {