Fixed [scenario] map_file basically being unusable

Automatically checking the path relative to a maps/ directory without binary
path support results in an invalid path almost every single time. If I remember
correctly from my testing, the only time that worked was if I added a data/maps
folder.

changelog.md

@@ -249,6 +249,7 @@
    * Fixed Lua errors when setting a music track that cannot be found when the
      playlist is already empty, e.g. if there's no music installed for the
      game (issue #3194).
+   * Fixed [scenario] map_file= being unusable in most circumstances.
 
 ## Version 1.13.12
  ### Security fixes

src/filesystem_common.cpp

@@ -138,12 +138,14 @@ bool ends_with(const std::string& str, const std::string& suffix)
 std::string read_map(const std::string& name)
 {
 	std::string res;
-	std::string map_location = get_wml_location("maps/" + name);
+	std::string map_location = get_wml_location(name);
 	if(!map_location.empty()) {
 		res = read_file(map_location);
 	}
 
-	if (res.empty()) {
+	// TODO: might be nice to have automatic detection of the maps/ directory?
+
+	if(res.empty()) {
 		res = read_file(get_user_data_dir() + "/editor/maps/" + name);
 	}