Add missing javadoc comment.

Author: raphw

byte-buddy-dep/src/main/java/net/bytebuddy/asm/MemberSubstitution.java

@@ -7068,6 +7068,9 @@ protected static class SubstitutingMethodVisitor extends LocalVariableAwareMetho
          */
         private int localVariableExtension;
 
+        /**
+         * {@code true} if at least one member was substituted during the application of this visitor.
+         */
         private boolean matched;
 
         /**