Fix more NULL guid reference handling instances.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/branches/gda-dev2@17420 57a11ea4-9604-0410-9ed3-97b8803252fd

src/business/business-core/sql/gnc-invoice-sql.c

@@ -245,7 +245,7 @@ load_invoice_guid( const GncSqlBackend* be, GncSqlRow* row,
 	g_return_if_fail( table_row != NULL );
 
     val = gnc_sql_row_get_value_at_col_name( row, table_row->col_name );
-    if( val == NULL ) {
+    if( val == NULL || !G_VALUE_HOLDS_STRING( val ) || g_value_get_string( val ) == NULL ) {
         pGuid = NULL;
     } else {
         string_to_guid( g_value_get_string( val ), &guid );

src/business/business-core/sql/gnc-order-sql.c

@@ -201,7 +201,7 @@ load_order_guid( const GncSqlBackend* be, GncSqlRow* row,
 	g_return_if_fail( table_row != NULL );
 
     val = gnc_sql_row_get_value_at_col_name( row, table_row->col_name );
-    if( val == NULL ) {
+    if( val == NULL || !G_VALUE_HOLDS_STRING( val ) || g_value_get_string( val ) == NULL ) {
         pGuid = NULL;
     } else {
         string_to_guid( g_value_get_string( val ), &guid );

src/business/business-core/sql/gnc-tax-table-sql.c

@@ -369,7 +369,7 @@ load_taxtable_guid( const GncSqlBackend* be, GncSqlRow* row,
 	g_return_if_fail( table_row != NULL );
 
     val = gnc_sql_row_get_value_at_col_name( row, table_row->col_name );
-    if( val == NULL ) {
+    if( val == NULL || !G_VALUE_HOLDS_STRING( val ) || g_value_get_string( val ) == NULL ) {
         pGuid = NULL;
     } else {
         string_to_guid( g_value_get_string( val ), &guid );