fix the isnan and isinf checking condition for marg_dist_stat background plot

reorganize the checking condition & message

take out z.sum() condition as it is not used

gstlal-inspiral/python/plots/far.py

@@ -102,10 +102,15 @@ def plot_snr_chi_pdf(rankingstat, instrument, which, chi_type, snr_max, event_sn
 	x = binnedarray.bins[0].centres()[:-1]
 	y = binnedarray.bins[1].centres()[:-1]
 	z = binnedarray.at_centres()[:-1,:-1]
+
+	# checking nan and inf
+	if numpy.isnan(z).all():
+		warnings.warn("%s %s is all NaN, skipping" % (instrument, which))
+		return None
+	if numpy.isinf(z).all():
+		warnings.warn("%s %s is all inf, skipping" % (instrument, which))
+		return None
 	if numpy.isnan(z).any():
-		if numpy.isnan(z).all():
-			warnings.warn("%s %s is all NaN, skipping" % (instrument, which))
-			return None
 		warnings.warn("%s %s contains NaNs" % (instrument, which))
 		z = numpy.ma.masked_where(numpy.isnan(z), z)