Fix fileobj I/O undeterministic behavior

Ever since the file-like object support was added in pytorch#1158, the test
was occasionally failing in CI. This PR fixes this.

Author: mthrok

third_party/sox/CMakeLists.txt

@@ -197,6 +197,7 @@ ExternalProject_Add(sox
   URL https://downloads.sourceforge.net/project/sox/sox/14.4.2/sox-14.4.2.tar.bz2
   URL_HASH SHA256=81a6956d4330e75b5827316e44ae381e6f1e8928003c6aa45896da9041ea149c
   CONFIGURE_COMMAND ${CMAKE_COMMAND} -E env ${envs} ${CMAKE_CURRENT_BINARY_DIR}/src/sox/configure ${COMMON_ARGS} ${SOX_OPTIONS}
+  PATCH_COMMAND patch < ${CMAKE_CURRENT_SOURCE_DIR}/patch/sox.patch
   BUILD_BYPRODUCTS ${SOX_LIBRARIES}
   DOWNLOAD_NO_PROGRESS ON
   LOG_DOWNLOAD ON

third_party/sox/patch/sox.patch

@@ -0,0 +1,14 @@
+diff -ru src/formats.c src/formats.c
+--- src/formats.c	2014-10-26 19:55:50.000000000 -0700
++++ src/formats.c	2021-02-22 16:01:02.833144070 -0800
+@@ -333,6 +333,9 @@
+   assert(ft);
+   if (!ft->fp)
+     return sox_false;
+-  fstat(fileno((FILE*)ft->fp), &st);
++  int fd = fileno((FILE*)ft->fp);
++  if (fd < 0)
++    return sox_false;
++  fstat(fd, &st);
+   return ((st.st_mode & S_IFMT) == S_IFREG);
+ }