os: don't close the Rm_connection in ldso

At this point we cannot close the connection anymore because all
mappings are gone and the needed stack is invalid. This is not a
problem since process will be discarded anyway.

Fixes #909.

os/src/lib/ldso/file.cc

@@ -41,6 +41,8 @@ namespace Genode {
 			Rm_area(addr_t base)
 			: Rm_connection(0, RESERVATION), _range(env()->heap())
 			{
+				on_destruction(KEEP_OPEN);
+
 				_base = (addr_t) env()->rm_session()->attach_at(dataspace(), base);
 				_range.add_range(base, RESERVATION);
 			}