dtc: trivial '-I fs -O dts' test

Some recent changes caused '-I fs -O dts' to crash instantly when
emitting the first property holding actual data, ie, coming from
a non-empty file. This got fixed already by another patch.

This simply adds a test for the original problem.

Signed-off-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/run_tests.sh

@@ -448,6 +448,11 @@ libfdt_tests () {
 
     run_test check_header test_tree1.dtb
 
+    rm -rf fstree
+    mkdir fstree
+    echo -n "foo" > fstree/non_empty_prop
+    run_dtc_test -I fs -O dts fstree
+
     # check full tests
     for good in test_tree1.dtb; do
 	run_test check_full $good