Show error message when validation fails

An error message is shown when validation of connection details to a
WebDAV server fails.
12 jobs for 200-the-app-shall-show-validation-errors-when-creating-a-new-library in 27 minutes and 54 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Images
manual #64275285
allowed to fail manual
build_image_android
manual #64275282
allowed to fail manual
build_image_ubuntu
manual #64275283
allowed to fail manual
build_image_win32
manual #64275284
allowed to fail manual
build_image_win64
 
  Build
passed #64275293
android_armv7

00:27:54

passed #64275294
android_x86

00:10:36

manual #64275292
macos allowed to fail manual
macos
passed #64275286
ubuntu_appimage

00:09:27

passed #64275287
win32_build

00:04:22

manual #64275289
windows allowed to fail manual
win32_vs_build
passed #64275288
win64_build

00:07:17

manual #64275291
windows allowed to fail manual
win64_vs_build