send-email, fix breakage in combination with --compose

This fixes the subtile bug in git send-email that was introduced into
git send-email with aa54892f5a (send-email:
detect invocation errors earlier), which caused no patches to be sent
out if the --compose flag was used.

Signed-off-by: Gustaf Hendeby <hendeby@isy.liu.se>
Tested-by: Seth Falcon <seth@userprimary.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -462,7 +462,7 @@ EOT
 		exit(0);
 	}
 
-	@files = ($compose_filename . ".final");
+	@files = ($compose_filename . ".final", @files);
 }
 
 # Variables we set as part of the loop over files