v4l2src: don't deref NULL

Error out when the pool gets shutdown.

ext/jpeg/gstjpegenc.c

@@ -517,6 +517,12 @@ gst_jpegenc_chain (GstPad * pad, GstBuffer * buf)
   jpegenc->jdest.next_output_byte = GST_BUFFER_DATA (jpegenc->output_buffer);
   jpegenc->jdest.free_in_buffer = GST_BUFFER_SIZE (jpegenc->output_buffer);
 
+  /* FIXME: shouldn't we also set
+   * - jpegenc->cinfo.max_{v,h}_samp_factor
+   * - jpegenc->cinfo.comp_info[0,1,2].{v,h}_samp_factor
+   * accordingly?
+   */
+
   /* prepare for raw input */
 #if JPEG_LIB_VERSION >= 70
   jpegenc->cinfo.do_fancy_downsampling = FALSE;

sys/v4l2/v4l2src_calls.c

@@ -105,6 +105,8 @@ gst_v4l2src_grab_frame (GstV4l2Src * v4l2src, GstBuffer ** buf)
 
   v4l2object = v4l2src->v4l2object;
   pool = v4l2src->pool;
+  if (!pool)
+    goto no_buffer_pool;
 
   GST_DEBUG_OBJECT (v4l2src, "grab frame");
 
@@ -174,6 +176,11 @@ gst_v4l2src_grab_frame (GstV4l2Src * v4l2src, GstBuffer ** buf)
   return GST_FLOW_OK;
 
   /* ERRORS */
+no_buffer_pool:
+  {
+    GST_DEBUG ("no buffer pool");
+    return GST_FLOW_WRONG_STATE;
+  }
 select_error:
   {
     GST_ELEMENT_ERROR (pool->v4l2elem, RESOURCE, READ, (NULL),

tests/check/Makefile.am

@@ -82,6 +82,7 @@ endif
 
 check_PROGRAMS = \
 	generic/states \
+	generic/capsrenegotiation \
 	$(check_annodex) \
 	elements/alphacolor \
 	elements/aspectratiocrop \