baseparse: Add unit test for short reads

Before the previous commit, buffer pulling count and chain function call
counts are not equal due to EOS. After the modification, these counts
are equal so unit test is passing.

gstreamer/gstreamer!33
gstreamer/gstreamer#294
3 jobs for master in 6 minutes and 38 seconds (queued for 15 minutes and 1 second)
Status Name Job ID Coverage
  Preparation
passed manifest #52353

00:00:19

 
  Build
passed build fedora x86_64 #52354

00:03:42

 
  Full Builds
passed build android arm64 api28 #52355

00:02:37