fix(server): add missing return after error responses (#2150)

In BeginAuthnRegistration (webauthn.go), missing return statements after
error responses caused the function to continue executing with a nil
authnInstance, potentially leading to a nil pointer panic.

In OIDCLoginCallback and SSOLoginCallback (ssologin.go), missing return
statements after GenerateToken/autoRegister errors caused the handler to
send a second response, resulting in a superfluous response write.

In SetThunderBrowser (offline_download.go), the default case of the
storage type switch sent an error response but did not return, causing
SaveSettingItems and tool initialization to continue executing even when
driver type validation failed.

server/handles/offline_download.go

@@ -448,6 +448,7 @@ func SetThunderBrowser(c *gin.Context) {
 		case *thunder_browser.ThunderBrowser, *thunder_browser.ThunderBrowserExpert:
 		default:
 			common.ErrorStrResp(c, "unsupported storage driver for offline download, only ThunderBrowser is supported", 400)
+			return
 		}
 	}
 	items := []model.SettingItem{

server/handles/ssologin.go

@@ -256,11 +256,13 @@ func OIDCLoginCallback(c *gin.Context) {
 			user, err = autoRegister(userID, userID, err)
 			if err != nil {
 				common.ErrorResp(c, err, 400)
+				return
 			}
 		}
 		token, err := common.GenerateToken(user)
 		if err != nil {
 			common.ErrorResp(c, err, 400)
+			return
 		}
 		if useCompatibility {
 			c.Redirect(302, common.GetApiUrl(c)+"/@login?token="+token)
@@ -427,6 +429,7 @@ func SSOLoginCallback(c *gin.Context) {
 	token, err := common.GenerateToken(user)
 	if err != nil {
 		common.ErrorResp(c, err, 400)
+		return
 	}
 	if usecompatibility {
 		c.Redirect(302, common.GetApiUrl(c)+"/@login?token="+token)

server/handles/webauthn.go

@@ -130,17 +130,20 @@ func BeginAuthnRegistration(c *gin.Context) {
 	authnInstance, err := authn.NewAuthnInstance(c)
 	if err != nil {
 		common.ErrorResp(c, err, 400)
+		return
 	}
 
 	options, sessionData, err := authnInstance.BeginRegistration(user)
 
 	if err != nil {
 		common.ErrorResp(c, err, 400)
+		return
 	}
 
 	val, err := json.Marshal(sessionData)
 	if err != nil {
 		common.ErrorResp(c, err, 400)
+		return
 	}
 
 	common.SuccessResp(c, gin.H{