Allow NULL module capability

The module will never be proved. This applies to the "main" module
and the playlist demux (which only has submodules).

src/libvlc-module.c

@@ -2811,7 +2811,6 @@ vlc_module_begin ()
     /* add_usage_hint( PLAYLIST_USAGE ) */
 
     set_description( N_("main program") )
-    set_capability( "main", 100 )
 vlc_module_end ()
 
 /*****************************************************************************

src/modules/entry.c

@@ -63,7 +63,7 @@ module_t *vlc_module_create (void)
     module->psz_help = NULL;
     module->pp_shortcuts = NULL;
     module->i_shortcuts = 0;
-    module->psz_capability = (char*)"";
+    module->psz_capability = NULL;
     module->i_score = 1;
     module->b_unloadable = true;
     module->pf_activate = NULL;

src/modules/modules.c

@@ -190,6 +190,8 @@ void module_LoadPlugins (vlc_object_t *obj)
  */
 bool module_provides( const module_t *m, const char *cap )
 {
+    if (unlikely(m->psz_capability == NULL))
+        return false;
     return !strcmp( m->psz_capability, cap );
 }
 
@@ -1071,7 +1073,8 @@ static void DupModule( module_t *p_module )
 
     /* We strdup() these entries so that they are still valid when the
      * module is unloaded. */
-    p_module->psz_capability = strdup( p_module->psz_capability );
+    p_module->psz_capability =
+        p_module->psz_capability ? strdup( p_module->psz_capability ) : NULL;
     p_module->psz_shortname = p_module->psz_shortname ?
                                  strdup( p_module->psz_shortname ) : NULL;
     p_module->psz_longname = strdup( p_module->psz_longname );