Guard restore variables against misconfigured shells

This applies the same idea from 44c6fe7
to the restore variables.

It is needed because some weird misconfigured shells may prefix every
shell output with some weird escape codes.

Fixes #52

Author: vimpostor

autoload/tpipeline.vim

@@ -141,8 +141,8 @@ endfunc
 
 func tpipeline#fork_job()
 	if g:tpipeline_restore
-		let s:restore_left = system("tmux display-message -p '#{status-left}'")
-		let s:restore_right = system("tmux display-message -p '#{status-right}'")
+		let s:restore_left = systemlist("sh -c 'echo \"\"; tmux display-message -p \"#{status-left}\"'")[-1]
+		let s:restore_right = systemlist("sh -c 'echo \"\"; tmux display-message -p \"#{status-right}\"'")[-1]
 	endif
 	let script = printf("while IFS='$\\n' read -r l; do echo \"$l\" > '%s'", s:tpipeline_filepath)
 	if g:tpipeline_usepane