_get_command_arguments: make trailing space optional

When pane_full_command has no arguments, the regex doesn't find argv[0]
as there is no trailing space.

For example, if pane_full_command was "vim" and the restore option was
"~Vim->vim *", the command "vim vim" would get executed instead of just
"vim".

Make the trailing space optional to match having only the command
without arguments.

scripts/process_restore_helpers.sh

@@ -121,7 +121,7 @@ _get_command_arguments() {
 	if _proc_starts_with_tildae "$match"; then
 		match="$(remove_first_char "$match")"
 	fi
-	echo "$pane_full_command" | sed "s,^.*${match}[^ ]* ,,"
+	echo "$pane_full_command" | sed "s,^.*${match}[^ ]* *,,"
 }
 
 _get_proc_restore_command() {