8242685: Better Path Validation

Reviewed-by: alanb, rhalade

Author: Brian Burkhalter

src/java.base/unix/classes/sun/nio/fs/UnixUriUtils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2008, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -83,7 +83,8 @@ static Path fromUri(UnixFileSystem fs, URI uri) {
                 if (b == 0)
                     throw new IllegalArgumentException("Nul character not allowed");
             } else {
-                assert c < 0x80;
+                if (c == 0 || c >= 0x80)
+                    throw new IllegalArgumentException("Bad escape");
                 b = (byte)c;
             }
             result[rlen++] = b;