Fix potential segfault (CID 252)

src/modules/modules.c

@@ -737,8 +737,10 @@ char ** module_GetModulesNamesForCapability( const char *psz_capability,
     {
         free( psz_ret );
         if( pppsz_longname )
+        {
             free( *pppsz_longname );
-        *pppsz_longname = NULL;
+            *pppsz_longname = NULL;
+        }
         module_list_free (list);
         return NULL;
     }