client: fix base path location deduction when sourced

- Since these files are only ever sourced, deduction must be relative to
  `BASH_SOURCE` (or else realpath will break)

- Fixes client-side `plugins` completion
  * realpath breakage was introduced in #301

client/conf.d/client/env/gen.bash

@@ -67,7 +67,7 @@ fi
 # Client-specific environment, including bind mounts (client view)
 
 if [ -z "$global_client_base_path" ]; then
-  global_client_base_path="$(dirname "$(realpath -s $0)" | rev | cut -d'/' -f3- | rev)"
+  global_client_base_path="$(realpath -s "${BASH_SOURCE[0]}" | rev | cut -d'/' -f7- | rev)"
 fi
 
 if [ -z "$DOCKER_FINANCE_CLIENT_CONF" ]; then