Fix using virtual layers in DB manager

getTableFields and getTableRowCount receive the table name and not the table. 
I did not change the argument name (although it would be good) to keep it in line with all the other methods

see:
https://github.com/qgis/QGIS/blob/master/python/plugins/db_manager/db_plugins/plugin.py#L742
https://github.com/qgis/QGIS/blob/master/python/plugins/db_manager/db_plugins/plugin.py#L879

Author: mbernasocchi

python/plugins/db_manager/db_plugins/vlayers/connector.py

@@ -250,16 +250,14 @@ def getRasterTables(self, schema=None):
         return []
 
     def getTableRowCount(self, table):
-        t = table[1]
-        l = VLayerRegistry.instance().getLayer(t)
+        l = VLayerRegistry.instance().getLayer(table)
         if not l or not l.isValid():
             return None
         return l.featureCount()
 
     def getTableFields(self, table):
         """ return list of columns in table """
-        t = table[1]
-        l = VLayerRegistry.instance().getLayer(t)
+        l = VLayerRegistry.instance().getLayer(table)
         if not l or not l.isValid():
             return []
         # id, name, type, nonnull, default, pk