t3901: avoid negation on right hand side of '|'

Some shells do not properly handle constructs of the form:

   spew_something | ! process_input

So rewrite this to be:

   spew_something | process_input; test $? != 0

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3901-i18n-patch.sh

@@ -19,7 +19,7 @@ check_encoding () {
 		8859)
 			grep "^encoding ISO-8859-1" ;;
 		*)
-			! grep "^encoding ISO-8859-1" ;;
+			grep "^encoding ISO-8859-1"; test "$?" != 0 ;;
 		esac || {
 			bad=1
 			break