This patch comes from Mika Ilmaranta who attched it to the bug
https://bugzilla.redhat.com/show_bug.cgi?id=1204139.

--- postfix-3.0.1/src/util/scan_dir.c	2015-04-21 20:44:19.985338673 +0300
+++ postfix-3.0.1/src/util/scan_dir.c.reset-errno-before-readdir	2015-04-21 20:47:32.791855824 +0300
@@ -78,6 +78,7 @@ 
 #endif
 #endif
 #include <string.h>
+#include <errno.h>
 
 /* Utility library. */
 
@@ -177,6 +178,8 @@ char   *scan_dir_next(SCAN_DIR *scan)
 #define STREQ(x,y)	(strcmp((x),(y)) == 0)
 
     if (info) {
+	/* Some implementations report spurious errors. */
+	errno = 0;
 	while ((dp = readdir(info->dir)) != 0) {
 	    if (STREQ(dp->d_name, ".") || STREQ(dp->d_name, "..")) {
 		if (msg_verbose > 1)