speex: Fix crash on Windows caused by cross-CRT issue

Use speex_header_free() to free memory which was allocated by
library. Cross-CRT issue should not happen on 1.17 Cerbero build
but might happen custom build or so.

Part-of: <gstreamer/gst-plugins-good!606>
28 jobs for !606 with speex-fix in 29 minutes and 33 seconds (queued for 3 seconds)
detached
Status Job ID Name Coverage
  Preparation
passed #2878349
gst indent

00:00:17

passed #2878347
manifest

00:00:32

 
  Build
passed #2878366
gstreamer
build cerbero cross-android universal

00:08:22

passed #2878373
gst-ios-13.2
build cerbero cross-ios universal

00:24:58

passed #2878368
gstreamer
build cerbero cross win32

00:06:30

passed #2878371
gstreamer
build cerbero cross win64

00:04:38

passed #2878364
gstreamer
build cerbero fedora x86_64

00:04:30

passed #2878372
gst-macos-10.15
build cerbero macos x86_64

00:13:58

passed #2878355
build clang fedora x86_64

00:06:56

manual #2878362
1809 windows docker allowed to fail manual
build msys2
passed #2878350
build nodebug fedora x86_64

00:06:12

passed #2878352
build static fedora x86_64

00:05:23

passed #2878354
build static nodebug fedora x86_64

00:04:09

passed #2879223
1809 windows docker
build vs2017 amd64

00:13:22

passed #2879222
1809 windows docker
build vs2017 x86

00:13:34

failed #2878357
1809 windows docker
build vs2017 amd64

00:13:22

failed #2878359
1809 windows docker
build vs2017 x86

00:13:22

 
  Test
passed #2878374
gstreamer
check fedora

00:06:59

passed #2878375
gstreamer
integration testsuites fedora 1/4

00:16:42

passed #2878376
gstreamer
integration testsuites fedora 2/4

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passed #2878377
gstreamer
integration testsuites fedora 3/4

00:14:52

passed #2878378
gstreamer
integration testsuites fedora 4/4

00:16:14

passed #2878380
gstreamer
valgrind bad

00:05:13

passed #2878381
gstreamer
valgrind ges

00:06:33

passed #2878379
gstreamer
valgrind good

00:09:09

 
  Integrate
passed #2878382
cross-android universal examples

00:06:35

passed #2878384
gst-ios-13.2
cross-ios universal examples

00:03:32

passed #2878383
documentation

00:08:01