am: don't infloop for an empty input file

git-am.sh's check_patch_format function would attempt to preview
the patch to guess its format, but would go into an infinite loop
when the patch file happened to be empty.  The solution: exit the
loop when "read" fails, not when the line var, "$l1" becomes empty.

Signed-off-by: Jim Meyering <meyering@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/git-am.sh b/git-am.sh
index 1c13b13991..f43a75b04b 100755
--- a/git-am.sh
+++ b/git-am.sh
@@ -201,7 +201,7 @@ check_patch_format () {
 		l1=
 		while test -z "$l1"
 		do
-			read l1
+			read l1 || break
 		done
 		read l2
 		read l3