[MM-29731] Fix panic in saveUserTermsOfService (#16044)

* Fix panic in saveUserTermsOfService

* Remove unneeded initialization

api4/user.go

@@ -2423,8 +2423,16 @@ func saveUserTermsOfService(c *Context, w http.ResponseWriter, r *http.Request)
 	props := model.StringInterfaceFromJson(r.Body)
 
 	userId := c.App.Session().UserId
-	termsOfServiceId := props["termsOfServiceId"].(string)
-	accepted := props["accepted"].(bool)
+	termsOfServiceId, ok := props["termsOfServiceId"].(string)
+	if !ok {
+		c.SetInvalidParam("termsOfServiceId")
+		return
+	}
+	accepted, ok := props["accepted"].(bool)
+	if !ok {
+		c.SetInvalidParam("accepted")
+		return
+	}
 
 	auditRec := c.MakeAuditRecord("saveUserTermsOfService", audit.Fail)
 	defer c.LogAuditRec(auditRec)