Remove install errors emitted when using jlibtool instead of GNU libtool.

(grep would skip this silently; but sed emits errors when no match is found.)

* build/instdso.sh: Protect sed calls with a test -s check to make sure
  that we're going to execute sed against a non-empty file.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@292109 13f79535-47bb-0310-9956-ffa450edef68