This check is necessery eg. for a bug in HP-UX 11 which can return bad value.

diff -ur gawk-3.1.1.orig/posix/gawkmisc.c gawk-3.1.1/posix/gawkmisc.c
--- gawk-3.1.1.orig/posix/gawkmisc.c	Tue Apr 16 13:58:41 2002
+++ gawk-3.1.1/posix/gawkmisc.c	Fri May 24 11:46:35 2002
@@ -77,7 +77,7 @@
 	 * meant for in the first place.
 	 */
 #ifdef HAVE_ST_BLKSIZE
-#define DEFBLKSIZE	(stb->st_blksize ? stb->st_blksize : BUFSIZ)
+#define DEFBLKSIZE	(stb->st_blksize > 0 ? stb->st_blksize : BUFSIZ)
 #else
 #define	DEFBLKSIZE	BUFSIZ
 #endif