h265parse: Fix and optimize NAL collection function

Adopt h264parse's _collect_nal() behavior.
See also commit 5601c87 and  https://bugzilla.gnome.org/show_bug.cgi?id=732154

https://bugzilla.gnome.org/show_bug.cgi?id=754124
diff --git a/gst/videoparsers/gsth265parse.c b/gst/videoparsers/gsth265parse.c
index d696e8d..0661c86 100644
--- a/gst/videoparsers/gsth265parse.c
+++ b/gst/videoparsers/gsth265parse.c
@@ -686,10 +686,10 @@
   GstH265NalUnit nnalu;
 
   GST_DEBUG_OBJECT (h265parse, "parsing collected nal");
-  parse_res = gst_h265_parser_identify_nalu (h265parse->nalparser, data,
-      nalu->offset + nalu->size, size, &nnalu);
+  parse_res = gst_h265_parser_identify_nalu_unchecked (h265parse->nalparser,
+      data, nalu->offset + nalu->size, size, &nnalu);
 
-  if (parse_res == GST_H265_PARSER_ERROR)
+  if (parse_res != GST_H265_PARSER_OK)
     return FALSE;
 
   /* determine if AU complete */