t0090: tweak awk statement for Solaris /usr/xpg4/bin/awk

t0090: tweak awk statement for Solaris /usr/xpg4/bin/awk

The awk statements previously used in this test weren't compatible
with the native versions of awk on Solaris:

    echo "dir" | /bin/awk -v c=0 '$1 {++c} END {print c}'
    awk: syntax error near line 1
    awk: bailing out near line 1

    echo "dir" | /usr/xpg4/bin/awk -v c=0 '$1 {++c} END {print c}'
    0

Even though we do not cater to tools in /usr/bin on Solaris that
have and are overridden by corresponding ones in /usr/xpg?/bin,
in this case, even the XPG version does not work correctly.

With GNU awk for comparison:

    echo "dir" | /opt/csw/gnu/awk -v c=0 '$1 {++c} END {print c}'
    1

which is what this test expects (and is in line with POSIX; non-empty
string is true and an empty string is false).

Work this issue around by using $1 != "" to state more explicitly
that we are skipping empty lines.

Helped-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Ben Walton <bdwalton@gmail.com>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>