Add error check comments.

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

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);
       }
    }