4808. [bug] Properly test for zlib.h. [RT #46504]

CHANGES

+4808.	[bug]		Properly test for zlib.h. [RT #46504]
+
 4807.	[cleanup]	isc_rng_randombytes() returns a specified number of
 			bytes from the PRNG; this is now used instead of
 			calling isc_rng_random() multiple times. [RT #46230]

configure.in

@@ -2652,7 +2652,7 @@ case "$with_zlib" in
 		done
 		;;
 	*)
-		if test -f "${with_zlib}/zlib.h"
+		if test -f "${with_zlib}/include/zlib.h"
 		then
 			zlib_cflags="-I${with_zlib}/include"
 			LIBS="$LIBS -L${with_zlib}/lib"