Do not panic in fini if init fails

Fixes #2

src/tests/r0002.vtc

+# looks like -*- perl -*-
+
+varnishtest "vcl.use and .discard, and version string"
+
+server s1 {
+} -start
+
+varnish v1 -vcl+backend {
+	import blobcode from "${vmod_topbuild}/src/.libs/libvmod_blobcode.so";
+} -start
+
+varnish v1 -errvcl {Failed initialization} {
+	import blobcode from "${vmod_topbuild}/src/.libs/libvmod_blobcode.so";
+
+	backend default {
+		.host = "127.0.0.1";
+	}
+
+	sub vcl_init {
+		return (fail);
+		new id = blobcode.blob(IDENTITY, "foo");
+	}
+}

src/vmod_blobcode.c

@@ -329,7 +329,9 @@ vmod_blob__fini(struct vmod_blobcode_blob **blobp)
 {
 	struct vmod_blobcode_blob *b;
 
-	AN(*blobp);
+	if (*blobp == NULL)
+		return;
+
 	b = *blobp;
 	*blobp = NULL;
 	CHECK_OBJ_NOTNULL(b, VMOD_BLOBCODE_BLOB_MAGIC);