[browser] Fix addition of PostGIS layers with unknown CRS

When a PostGIS table does not have CRS specified (srid == 0) then
it was not possible to correctly load it from browser (but it worked
from DB manager). The problem was that browser item used negative
srid in layer URI, messing up everything.

Also fixed the display of srid in tooltip (it says "unknown" rather
than showing -2147483648)

src/providers/postgres/qgspostgresdataitems.cpp

@@ -516,7 +516,7 @@ QString QgsPGLayerItem::createUri()
 
   uri.setDataSource( mLayerProperty.schemaName, mLayerProperty.tableName, mLayerProperty.geometryColName, mLayerProperty.sql, cols.join( ',' ) );
   uri.setWkbType( mLayerProperty.types.at( 0 ) );
-  if ( uri.wkbType() != QgsWkbTypes::NoGeometry )
+  if ( uri.wkbType() != QgsWkbTypes::NoGeometry && mLayerProperty.srids.at( 0 ) != std::numeric_limits<int>::min() )
     uri.setSrid( QString::number( mLayerProperty.srids.at( 0 ) ) );
   QgsDebugMsg( QStringLiteral( "layer uri: %1" ).arg( uri.uri( false ) ) );
   return uri.uri( false );
@@ -750,7 +750,12 @@ QgsPGLayerItem *QgsPGSchemaItem::createLayer( QgsPostgresLayerProperty layerProp
     tip = tr( "Table" );
   }
   QgsWkbTypes::Type wkbType = layerProperty.types.at( 0 );
-  tip += tr( "\n%1 as %2 in %3" ).arg( layerProperty.geometryColName, QgsPostgresConn::displayStringForWkbType( wkbType ) ).arg( layerProperty.srids.at( 0 ) );
+  tip += tr( "\n%1 as %2" ).arg( layerProperty.geometryColName, QgsPostgresConn::displayStringForWkbType( wkbType ) );
+  if ( layerProperty.srids.at( 0 ) != std::numeric_limits<int>::min() )
+    tip += tr( " (srid %1)" ).arg( layerProperty.srids.at( 0 ) );
+  else
+    tip += tr( " (unknown srid)" );
+
   if ( !layerProperty.tableComment.isEmpty() )
   {
     tip = layerProperty.tableComment + '\n' + tip;