generate web error when opening an invalid public file link (#7475)

api/file.go

@@ -177,10 +177,12 @@ func getPublicFile(c *Context, w http.ResponseWriter, r *http.Request) {
 
 		if hash != correctHash {
 			c.Err = model.NewAppError("getPublicFile", "api.file.get_file.public_invalid.app_error", nil, "", http.StatusBadRequest)
+			http.Redirect(w, r, c.GetSiteURLHeader()+"/error?message="+utils.T(c.Err.Message), http.StatusTemporaryRedirect)
 			return
 		}
 	} else {
 		c.Err = model.NewAppError("getPublicFile", "api.file.get_file.public_invalid.app_error", nil, "", http.StatusBadRequest)
+		http.Redirect(w, r, c.GetSiteURLHeader()+"/error?message="+utils.T(c.Err.Message), http.StatusTemporaryRedirect)
 		return
 	}
 
@@ -251,10 +253,12 @@ func getPublicFileOld(c *Context, w http.ResponseWriter, r *http.Request) {
 
 		if hash != correctHash {
 			c.Err = model.NewAppError("getPublicFile", "api.file.get_file.public_invalid.app_error", nil, "", http.StatusBadRequest)
+			http.Redirect(w, r, c.GetSiteURLHeader()+"/error?message="+utils.T(c.Err.Message), http.StatusTemporaryRedirect)
 			return
 		}
 	} else {
 		c.Err = model.NewAppError("getPublicFile", "api.file.get_file.public_invalid.app_error", nil, "", http.StatusBadRequest)
+		http.Redirect(w, r, c.GetSiteURLHeader()+"/error?message="+utils.T(c.Err.Message), http.StatusTemporaryRedirect)
 		return
 	}