xxd: fix -p -r, closes 13881

function                                             old     new   delta
xxd_main                                             893     890      -3

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

testsuite/xxd.tests

@@ -31,4 +31,10 @@ testing 'xxd -p with 31 NULs' \
 	'' \
 	'\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0'
 
+testing 'xxd -p -r' \
+	'xxd -p -r' \
+	'01234567765432100123456776543210' \
+	'' \
+	'30313233343536373736353433323130 30313233343536373736353433323130'
+
 exit $FAILCOUNT