tests: Fix runtime error in test-authz-pam

A test with sanitizers on macOS shows this error:

    authz/pamacct.c:50:25: runtime error: null pointer passed as argument 1, which is declared to never be null
    /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/security/pam_appl.h:56:2: note: nonnull attribute specified here

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

tests/test-authz-pam.c

@@ -28,7 +28,7 @@
 static bool failauth;
 
 /*
- * These two functions are exported by libpam.so.
+ * These three functions are exported by libpam.so.
  *
  * By defining them again here, our impls are resolved
  * by the linker instead of those in libpam.so
@@ -50,6 +50,7 @@ pam_start(const char *service_name, const char *user,
         failauth = false;
     }
 
+    *pamh = (pam_handle_t *)0xbadeaffe;
     return PAM_SUCCESS;
 }
 
@@ -65,6 +66,13 @@ pam_acct_mgmt(pam_handle_t *pamh, int flags)
 }
 
 
+int
+pam_end(pam_handle_t *pamh, int status)
+{
+    return PAM_SUCCESS;
+}
+
+
 static void test_authz_unknown_service(void)
 {
     Error *local_err = NULL;