Prevent leaving unparsed tokens ignored, throwing error instead.

src/main/java/org/nwapw/abacus/parsing/ShuntingYardParser.java

@@ -164,7 +164,8 @@ public class ShuntingYardParser implements Parser<Match<TokenType>>, PluginListe
         tokens = intoPostfix(new ArrayList<>(tokens));
         if(tokens == null) return null;
         Collections.reverse(tokens);
-        return constructRecursive(tokens);
+        TreeNode constructedTree = constructRecursive(tokens);
+        return tokens.size() == 0 ? constructedTree : null;
     }
 
     @Override