gstbasetransform: fix for element going away while receiving a query

Before this could lead to the trans->sinkpad and ->srcpad being
invalid when used.
21 jobs for basetrans-missing-pad-on-query in 152 minutes and 18 seconds (queued for 14 minutes and 32 seconds)
latest
Status Job ID Name Coverage
  Preparation
passed #356885
gst indent

00:00:16

passed #356884
manifest

00:00:52

 
  Build
passed #356886
build fedora x86_64

00:05:29

passed #356887
build nodebug fedora x86_64

00:04:21

passed #356888
build static fedora x86_64

00:13:50

passed #356889
build static nodebug fedora x86_64

00:13:02

 
  Test
passed #356890
check fedora

00:03:59

passed #356891
integration testsuites fedora

00:09:20

 
  Full Builds
passed #356893
build cerbero android universal

00:12:58

passed #356894
build cerbero cross win32

00:07:51

passed #356895
build cerbero cross win64

00:06:00

passed #356892
build cerbero fedora x86_64

00:08:10

passed #356896
gst-macos-10.14
build cerbero macos x86_64

00:08:00

 
  Full Tests
passed #356901
valgrind bad

00:06:33

passed #356898
valgrind base

00:07:21

passed #356897
valgrind core

00:11:30

passed #356902
valgrind ges

00:06:54

passed #356899
valgrind good

00:10:04

passed #356900
valgrind ugly

00:02:05

 
  Apps
passed #356903
android universal examples

00:08:50

 
  Deploy
passed #356904
documentation

00:04:43