DBManager topoviewer: don't be fooled by srid=-1 in topology.topology

Fixes #12802

python/plugins/db_manager/db_plugins/postgis/plugins/qgis_topoview/__init__.py

@@ -86,7 +86,11 @@ def run(item, action, mainwindow):
                                        mainwindow.iface.messageTimeout())
         return False
 
-    toposrid = str(res[0])
+    if ( res[0] < 0 ):
+        mainwindow.infoBar.pushMessage("WARNING", u'Topology "{0}" is registered as having a srid of {1} in topology.topology, we will assume 0 (for unknown)'.format(item.schema().name, res[0]), QgsMessageBar.WARNING, mainwindow.iface.messageTimeout())
+        toposrid = '0'
+    else:
+        toposrid = str(res[0])
 
     # load layers into the current project
     toponame = item.schema().name