Select -1 as `state' for history queries not providing a valid state

PostgreSQL does not seem to be able to union null values with
integers...

refs #9009

modules/monitoring/library/Monitoring/Backend/Ido/Query/HostcommenthistoryQuery.php

@@ -26,7 +26,7 @@ class HostcommenthistoryQuery extends IdoQuery
             'type'      => "(CASE hch.entry_type WHEN 1 THEN 'comment' WHEN 2 THEN 'dt_comment' WHEN 3 THEN 'flapping' WHEN 4 THEN 'ack' END)",
             'timestamp' => 'UNIX_TIMESTAMP(hch.comment_time)',
             'object_id' => 'hch.object_id',
-            'state'     => '(NULL)',
+            'state'     => '(-1)',
             'output'    => "('[' || hch.author_name || '] ' || hch.comment_data)",
         ),
         'hostgroups' => array(

modules/monitoring/library/Monitoring/Backend/Ido/Query/HostdowntimestarthistoryQuery.php

@@ -26,7 +26,7 @@ class HostdowntimestarthistoryQuery extends IdoQuery
             'type'      => "('dt_start')",
             'timestamp' => 'UNIX_TIMESTAMP(hdh.actual_start_time)',
             'object_id' => 'hdh.object_id',
-            'state'     => '(NULL)',
+            'state'     => '(-1)',
             'output'    => "('[' || hdh.author_name || '] ' || hdh.comment_data)",
         ),
         'hostgroups' => array(

modules/monitoring/library/Monitoring/Backend/Ido/Query/ServicecommenthistoryQuery.php

@@ -30,7 +30,7 @@ class ServicecommenthistoryQuery extends IdoQuery
             'type'      => "(CASE sch.entry_type WHEN 1 THEN 'comment' WHEN 2 THEN 'dt_comment' WHEN 3 THEN 'flapping' WHEN 4 THEN 'ack' END)",
             'timestamp' => 'UNIX_TIMESTAMP(sch.comment_time)',
             'object_id' => 'sch.object_id',
-            'state'     => '(NULL)',
+            'state'     => '(-1)',
             'output'    => "('[' || sch.author_name || '] ' || sch.comment_data)",
         ),
         'hostgroups' => array(

modules/monitoring/library/Monitoring/Backend/Ido/Query/ServicedowntimestarthistoryQuery.php

@@ -30,7 +30,7 @@ class ServicedowntimestarthistoryQuery extends IdoQuery
             'type'      => "('dt_start')",
             'timestamp' => 'UNIX_TIMESTAMP(sdh.actual_start_time)',
             'object_id' => 'sdh.object_id',
-            'state'     => '(NULL)',
+            'state'     => '(-1)',
             'output'    => "('[' || sdh.author_name || '] ' || sdh.comment_data)",
         ),
         'hostgroups' => array(