also ignore whitespace-only lines in db files

src/gen/gen_dcs_classifier.pl

@@ -746,7 +746,7 @@ for (my $i = 0; $i <= $#dbrefs; $i++) {
 	}
 
 	# ignore empty lines
-	next if (/^$/);
+	next if (/^\s*$/);
 
 	my ($key, $type) = split(/\t/, $_);