t9001: avoid including non-trailing NUL bytes in variables

In this test, we have a command substitution whose output starts with a
NUL byte.  bash and dash strip out any NUL bytes from the output; zsh
does not.  As a consequence, zsh fails this test, since the command line
argument we use the variable in is truncated by the NUL byte.

POSIX says of a command substitution that if "the output contains any
null bytes, the behavior is unspecified," so all of the shells are in
compliance with POSIX.  To make our code more portable, let's avoid
prefacing our variables with NUL bytes and instead leave only the
trailing one behind.

Signed-off-by: brian m. carlson <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: bk2204

t/t9001-send-email.sh

@@ -2066,7 +2066,7 @@ test_expect_success $PREREQ 'leading and trailing whitespaces are removed' '
 	TO1=$(echo "QTo 1 <[email protected]>" | q_to_tab) &&
 	TO2=$(echo "QZto2" | qz_to_tab_space) &&
 	CC1=$(echo "cc1" | append_cr) &&
-	BCC1=$(echo "Q [email protected] Q" | q_to_nul) &&
+	BCC1=$(echo " [email protected] Q" | q_to_nul) &&
 	git send-email \
 	--dry-run \
 	--from="	Example <[email protected]>" \