gstlal_string_triggergen: transform() error checking tweak

- move the check for odd-lengthed autocorrelation vectors to the top to serve the dual-purpose of also checking for missing autocorrelation vectors

gstlal-burst/gst/lal/gstlal_string_triggergen.c

@@ -209,6 +209,15 @@ static GstFlowReturn trigger_generator(GSTLALStringTriggergen *element, GstBuffe
 	guint sample;
 	gint channel;
 
+	/* check that autocorrelation vector has odd number of samples.
+	 * NOTE:  autocorrelation_length() returns 0 if the
+	 * autocorrelation_matrix is not set, so this g_assert also tests
+	 * for a missing autocorrelation_matrix.  in set_property(), if the
+	 * conversion from GValueArray fails the matrix will be left set to
+	 * NULL, so this is also catching those failures. */
+	g_assert(autocorrelation_length(element->autocorrelation_matrix) & 1);
+
+	/* do we have enough SNR to search for triggers? */
 	length = get_available_samples(element);
 	if(length < autocorrelation_length(element->autocorrelation_matrix)) {
 		/* FIXME:  PTS and duration are not necessarily correct.
@@ -237,9 +246,6 @@ static GstFlowReturn trigger_generator(GSTLALStringTriggergen *element, GstBuffe
 	if(!element->autocorrelation_norm)
 		element->autocorrelation_norm = gstlal_autocorrelation_chi2_compute_norms_string(element->autocorrelation_matrix, NULL);
 
-	/* check that autocorrelation vector has odd number of samples */
-	g_assert(autocorrelation_length(element->autocorrelation_matrix) & 1);
-
 	/* find events.  earliest sample that can be a new trigger starts a
 	 * little bit in from the start of the adapter because we are
 	 * re-using data from the last iteration for \chi^2 calculation.