api: fix missing silence initialization
api: fix missing silence initialization

brancz/alertmanager,tinytub/alertmanager,tbouvet/alertmanager,tbouvet/alertmanager,brunoqc/alertmanager,GoogleCloudPlatform/alertmanager,prometheus/alertmanager,Kellel/alertmanager,brunoqc/alertmanager,GoogleCloudPlatform/alertmanager,tyrken/alertmanager,GoogleCloudPlatform/alertmanager,tyrken/alertmanager,tbouvet/alertmanager,joehandzik/alertmanager,GoogleCloudPlatform/alertmanager,joehandzik/alertmanager,tyrken/alertmanager,tinytub/alertmanager,tyrken/alertmanager,brancz/alertmanager,Aloomaio/alertmanager,brunoqc/alertmanager,prometheus/alertmanager,brancz/alertmanager,joehandzik/alertmanager,prometheus/alertmanager,Kellel/alertmanager,Aloomaio/alertmanager,Aloomaio/alertmanager,brancz/alertmanager,Kellel/alertmanager,prometheus/alertmanager,brunoqc/alertmanager,tinytub/alertmanager