aggregator: Don't clear the pad's segment on flush

Normally, the segment field is only updated before aggregate is called,
but a flush would clear it immediately. This messes with subclasses
trying to use the segment after popping a buffer.

Leaving it around should be safe.
34 jobs for aggregator-keep-segment in 45 seconds (queued for 5 seconds)
latest
Status Job ID Name Coverage
  Build Docker
passed #4376597
alpine amd64 manifest builder docker

00:00:14

passed #4376596
android docker

00:00:14

passed #4376595
cerbero fedora amd64 docker

00:00:14

passed #4376594
fedora amd64 docker

00:00:13

passed #4376598
gst-indent amd64 docker

00:00:33

 
  Preparation
passed #4376600
gst indent

00:00:10

manual #4376599
manual
manifest
 
  Build
created #4376609
gstreamer
build cerbero cross-android universal
created #4376613
gst-ios-13.2
build cerbero cross-ios universal
created #4376610
gstreamer
build cerbero cross win32
created #4376611
gstreamer
build cerbero cross win64
created #4376608
gstreamer
build cerbero fedora x86_64
created #4376612
gst-macos-10.15
build cerbero macos x86_64
created #4376604
build clang fedora x86_64
created #4376607
1809 windows docker allowed to fail manual
build msys2
created #4376601
build nodebug fedora x86_64
created #4376602
build static fedora x86_64
created #4376603
build static nodebug fedora x86_64
created #4376605
1809 windows docker
build vs2017 amd64
created #4376606
1809 windows docker
build vs2017 x86
 
  Test
created #4376614
gstreamer
check fedora
created #4376615
gstreamer
integration testsuites fedora 1/4
created #4376616
gstreamer
integration testsuites fedora 2/4
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gstreamer
integration testsuites fedora 3/4
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gstreamer
integration testsuites fedora 4/4
created #4376623
gstreamer
valgrind bad
created #4376620
gstreamer
valgrind base
created #4376619
gstreamer
valgrind core
created #4376624
gstreamer
valgrind ges
created #4376621
gstreamer
valgrind good
created #4376622
gstreamer
valgrind ugly
 
  Integrate
created #4376625
cross-android universal examples
created #4376627
gst-ios-13.2
cross-ios universal examples
created #4376626
documentation