#1248 Discovery being called on a failed plugin

[Renier Morales]

This can cause segfaults if plugin code does not check for a null reference.

oh_discovery() should not run on failed plugins.

Fix is:

Index: src/plugin.c

--- src/plugin.c (revision 6423)
+++ src/plugin.c (working copy)
@@ -703,7 +703,7 @@
break;
}

- if (h->abi->discover_resources != NULL) {
+ if (h->abi->discover_resources && h->hnd) {
cur_error = h->abi->discover_resources(h->hnd);
if (cur_error == SA_OK && error) {
error = cur_error;