Add function to handle Excel formatting of sponsorship

When exporting issues in Excel format a fatal error is thrown if the
export includes sponsorship totals. This is due to a missing
excel_format_sponsorship_total() function.

Fixes #13959

core/excel_api.php

@@ -506,7 +506,7 @@ function excel_format_custom_field( $p_bug ) {
  */
 function excel_format_plugin_column_value( $p_column, $p_bug ) {
 	$t_plugin_columns = columns_get_plugin_columns();
-	
+
 	if ( !isset( $t_plugin_columns[$p_column] ) ) {
 		return excel_prepare_string( '' );
 	} else {
@@ -527,6 +527,16 @@ function excel_format_due_date( $p_bug ) {
 	return excel_prepare_string( date( config_get( 'short_date_format' ), $p_bug->due_date ) );
 }
 
+/**
+ * Gets the sponsorship total for an issue
+ * @param object $p_bug the bug
+ * @return string
+ * @access public
+ */
+function excel_format_sponsorship_total( $p_bug ) {
+	return excel_prepare_string( $p_bug->sponsorship_total );
+}
+
 /**
  * The <tt>ExcelStyle</tt> class is able to render style information
  *