[BUGFIX] Fix crash if sg_seo is not installed

ext_tables.sql

@@ -22,3 +22,8 @@ CREATE TABLE tx_sgnews_domain_model_author (
 	path_segment text,
 	image int(11) unsigned DEFAULT '0'
 );
+
+-- also set the tx_sgseo field here in order to fix the dependency
+CREATE TABLE pages (
+    tx_sgseo_schemajson mediumtext
+);