nuget-to-nix: catch errors from process substitution

Changed files
+1
pkgs
build-support
dotnet
nuget-to-nix
+1
pkgs/build-support/dotnet/nuget-to-nix/nuget-to-nix.sh
···
export DOTNET_CLI_TELEMETRY_OPTOUT=1
mapfile -t sources < <(dotnet nuget list source --format short | awk '/^E / { print $2 }')
+
wait "$!"
declare -a remote_sources
declare -A base_addresses