Clear loaded scenario blacklist when leaving world

This caused you to be unable to load a world with a mod containing a
scenario blacklist more than once without exiting the game.

Also don't locally redefine all_scenarios when finalizing scenario
blacklists.

src/init.cpp

@@ -512,6 +512,7 @@ void DynamicDataLoader::unload_data()
     reset_mapgens();
     reset_effect_types();
     reset_speech();
+    reset_scenarios_blacklist();
     overmap_land_use_codes::reset();
     overmap_connections::reset();
     overmap_locations::reset();

src/scenario.cpp

@@ -257,12 +257,12 @@ void scen_blacklist::load( const JsonObject &jo, const std::string & )
 
 void scen_blacklist::finalize()
 {
-    std::vector<string_id<scenario>> all_scenarios;
+    std::vector<string_id<scenario>> all_scens;
     for( const scenario &scen : scenario::get_all() ) {
-        all_scenarios.emplace_back( scen.ident() );
+        all_scens.emplace_back( scen.ident() );
     }
     for( const string_id<scenario> &sc : sc_blacklist.scenarios ) {
-        if( std::find( all_scenarios.begin(), all_scenarios.end(), sc ) == all_scenarios.end() ) {
+        if( std::find( all_scens.begin(), all_scens.end(), sc ) == all_scens.end() ) {
             debugmsg( "Scenario blacklist contains invalid scenario" );
         }
     }
@@ -283,6 +283,11 @@ void scen_blacklist::finalize()
     }
 }
 
+void reset_scenarios_blacklist()
+{
+    sc_blacklist.scenarios.clear();
+}
+
 std::vector<string_id<profession>> scenario::permitted_professions() const
 {
     if( !cached_permitted_professions.empty() ) {

src/scenario.h

@@ -119,4 +119,6 @@ struct scen_blacklist {
     void finalize();
 };
 
+void reset_scenarios_blacklist();
+
 #endif