Fix opening .class files

Author: rcx

src/main/java/club/bytecode/the/jda/FileContainer.java

@@ -36,6 +36,9 @@ public ClassNode loadClassFile(String filename) {
 
     public String findClassfile(String className) {
         String candidate = className + ".class";
+        if (name.endsWith(".class")) { // this is a single .class file. we need to strip the package path out.
+            candidate = JDA.getClassName(candidate);
+        }
         if (files.containsKey(candidate))
             return candidate;
         return "";

src/main/java/club/bytecode/the/jda/JDA.java

@@ -270,6 +270,11 @@ public static String getClassFilePath(String fileName) {
         return fileName.replace(File.separator, "/").substring(0, fileName.length() - ".class".length());
     }
 
+    /**
+     * Returns the last part of a fully qualified name, e.g. the class name.
+     * @param fullyQualifiedName a fully qualified name like "java/lang/String"
+     * @return just the name without the package name, e.g. "String"
+     */
     public static String getClassName(String fullyQualifiedName) {
         return fullyQualifiedName.substring(fullyQualifiedName.lastIndexOf('/') + 1);
     }