lint fix: staticcheck and null derefs

src/ifmib/ifmib_test.go

@@ -14,6 +14,7 @@ func TestNewInterfaceMIB(t *testing.T) {
 
 	if mib == nil {
 		t.Fatal("NewInterfaceMIB returned nil")
+		return
 	}
 
 	if mib.handler == nil {

src/vpp/vpp_iface_test.go

@@ -15,6 +15,7 @@ func TestNewInterfaceManager(t *testing.T) {
 
 	if manager == nil {
 		t.Fatal("NewInterfaceManager() returned nil")
+		return
 	}
 
 	if manager.client != client {
@@ -32,7 +33,6 @@ func TestNewInterfaceManager(t *testing.T) {
 	if manager.watchingEvents {
 		t.Error("InterfaceManager should not be watching events initially")
 	}
-
 }
 
 func TestInterfaceManagerSetEventCallback(t *testing.T) {

src/vpp/vpp_stats_test.go

@@ -15,6 +15,7 @@ func TestNewStatsManager(t *testing.T) {
 
 	if manager == nil {
 		t.Fatal("NewStatsManager() returned nil")
+		return
 	}
 
 	if manager.client != client {