check for failure on that mysql query (#2105)

physical/mysql.go

@@ -173,6 +173,9 @@ func (m *MySQLBackend) List(prefix string) ([]string, error) {
 	// Add the % wildcard to the prefix to do the prefix search
 	likePrefix := prefix + "%"
 	rows, err := m.statements["list"].Query(likePrefix)
+	if err != nil {
+		return nil, fmt.Errorf("failed to execute statement: %v", err)
+	}
 
 	var keys []string
 	for rows.Next() {