Fix some issues when loading new-format scenarios

- Carriage returns misinterpreted as map features
- Error code returned by CopyFiles
- Confusing error message when a file is missing in the archive

src/tools/fileio_scen.cpp

@@ -296,6 +296,7 @@ bool load_scenario_v1(fs::path file_to_load, cScenario& scenario, bool only_head
 }
 
 ticpp::Document xmlDocFromStream(std::istream& stream, std::string name) {
+	if(!stream) throw std::string("Error loading scenario file: ") + name;
 	std::string contents;
 	stream.seekg(0, std::ios::end);
 	contents.reserve(stream.tellg());

src/tools/map_parse.cpp

@@ -30,7 +30,7 @@ map_data load_map(std::istream& fin, bool isTown, std::string name) {
 		bool vehicle_owned;
 		for(char c : line) {
 			if(c == '#') break; // Found a comment
-			if(c == ' ' || c == '\t') continue;
+			if(isspace(c)) continue;
 			if(isdigit(c)) {
 				n *= 10;
 				n += c - '0';