CI: Clean in ../libpcap only if present. [skip ci]

./build_matrix.sh[89]: cd: /export/home/denis/libpcap: [No such file or
  directory]

diff --git a/build_matrix.sh b/build_matrix.sh
index c5f699a0c177864b159cff4351177334fd3747a8..b16e03e5e00d55ba3a38a5f5c13d79bfde1d7a01 100755 (executable)
--- a/build_matrix.sh
+++ b/build_matrix.sh
@@ -86,7 +86,9 @@ for CC in $MATRIX_CC; do
         else
             echo_magenta 'Use system libpcap' >&2
             purge_directory "$PREFIX"
-            (cd ../libpcap; make distclean || echo '(Ignoring the make error.)')
+            if [ -d ../libpcap ]; then
+                (cd ../libpcap; make distclean || echo '(Ignoring the make error.)')
+            fi
             build_tcpdump
         fi
     done