gst/: Aplied part of patch #157127: Cleanup of issues reported by sparse.

gst/: Aplied part of patch #157127: Cleanup of issues reported by sparse.

Original commit message from CVS:
reviewed by: Wim Taymans, Ronald Bultje.

* gst/cothreads.c: (cothread_create):
* gst/gstbin.c: (gst_bin_add_func), (gst_bin_remove_func),
(gst_bin_child_state_change_func):
* gst/gstbuffer.c: (gst_buffer_span):
* gst/gstelement.c: (gst_element_get_index),
(gst_element_get_event_masks), (gst_element_get_query_types),
(gst_element_get_formats):
* gst/gsterror.c: (_gst_core_errors_init),
(_gst_library_errors_init), (_gst_resource_errors_init),
(_gst_stream_errors_init):
* gst/gstobject.c: (gst_object_default_deep_notify):
* gst/gstpad.c: (gst_pad_get_event_masks),
(gst_pad_get_internal_links_default):
* gst/gstplugin.c: (gst_plugin_register_func),
(gst_plugin_get_module):
* gst/gststructure.c: (gst_structure_get_string),
(gst_structure_get_abbrs), (gst_structure_from_abbr),
(gst_structure_to_abbr):
* gst/gstutils.c: (gst_print_element_args):
* gst/schedulers/gstoptimalscheduler.c: (add_to_group),
(setup_group_scheduler), (gst_opt_scheduler_iterate):
Aplied part of patch #157127: Cleanup of issues reported by
sparse.
Also do not try to use cothreads when there is no cothread
context yet.