medialibrary: thumbnailer: include stdexcept for runtime_error

std::runtime_error is used in the code and stdexcept available through
transitive inclusion from medialibrary headers, but it might not be and
it is much safer to include it ourselves.
13 jobs for !16 with msvcrt in 80 minutes and 45 seconds (queued for 45 seconds)
latest detached
Status Job ID Name Coverage
  Build
canceled #400613
amd64 docker
android-arm

passed #400614
amd64 docker
android-arm64

00:15:07

canceled #400615
amd64 docker
android-x86

passed #400616
amd64 docker
android-x86_64

00:11:21

passed #400607
amd64 docker
debian

00:11:22

passed #400611
macos
ios-arm64

00:40:09

canceled #400612
macos
ios-armv7

passed #400610
macos
macos

00:48:08

passed #400609
amd64 docker
raspbian-arm

00:07:36

passed #400608
amd64 docker
snap

00:24:02

passed #400604
amd64 docker
win32

00:20:19

passed #400605
amd64 docker
win64

00:18:59

passed #400606
amd64 docker
win64-llvm

00:19:28