libs: postproc: fix a memory leak point.

filter_ops and filter_formats should already have valid value when
the function gst_vaapipostproc_ensure_filter_caps re-enter
13 jobs for fix_two_leak in 45 minutes and 55 seconds (queued for 9 seconds)
Status Job ID Name Coverage
  Preparation
passed #540998
gst indent

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passed #540997
manifest

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  Build
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build fedora x86_64

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passed #541005
docker windows 1607
build msys2

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build nodebug fedora x86_64

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build static fedora x86_64

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build static nodebug fedora x86_64

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docker windows 1607
build vs2017 amd64

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passed #541004
docker windows 1607
build vs2017 x86

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  Test
passed #543527
check fedora

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check fedora

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check fedora

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  Integrate
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documentation

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