tests: Add missing unrefs of objects after use

Unreffing the objects returned by gst_bin_get_by_name() and
gst_pipeline_get_use() were missing in several tests, so add these.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=734345
utils: Ghostpads can be request pads too but check if the pad has a template

Otherwise we dereference NULL in some cases and crash.
bytereader: use unchecked inline variant for get_remaining in more places

We've already done the g_return_*_if_fail (reader != NULL)
dance in those places, so no need to do it again.
examples: controller: fix typo in comments