gst/level/gstlevel.*: figure out if we're initialized directly instead of keeping a variable that's wrong in 90% of c...

Original commit message from CVS:
* gst/level/gstlevel.c: (gst_level_link), (gst_level_chain),
(gst_level_change_state), (gst_level_init):
* gst/level/gstlevel.h:
figure out if we're initialized directly instead of keeping a
variable that's wrong in 90% of cases
don't initialize pads and then leak them and use a new unitialized
pad. (fixes #142084)
these were bugs so n00bish I didn't find them for an hour :/