chpst: fix "envdir dir" case (bug 4574).

diff --git a/runit/chpst.c b/runit/chpst.c
index 6e5180b..43e8d5f 100644
--- a/runit/chpst.c
+++ b/runit/chpst.c
@@ -228,7 +228,7 @@
 	}
 
 	// envuidgid?
-	if (ENABLE_ENVUIDGID && applet_name[0] == 'e') {
+	if (ENABLE_ENVUIDGID && applet_name[0] == 'e' && applet_name[3] == 'u') {
 		env_user = *argv++;
 		opt |= OPT_U;
 	}