Fix URLClassLoader.patch to actually work

debian/patches/URLClassLoader.patch

 From: Markus Koschany <apo@debian.org>
 Date: Mon, 25 Mar 2019 14:44:22 +0100
-Bug-Debian: https://bugs.debian.org/923759
 Subject: URLClassLoader
 
 ---
  src/org/netlib/generate/JavaGenerator.java | 14 ++++++++++++--
  1 file changed, 12 insertions(+), 2 deletions(-)
 
-diff --git a/src/org/netlib/generate/JavaGenerator.java b/src/org/netlib/generate/JavaGenerator.java
-index fda8e9d..15815de 100644
---- a/src/org/netlib/generate/JavaGenerator.java
-+++ b/src/org/netlib/generate/JavaGenerator.java
+Index: netlib-java/src/org/netlib/generate/JavaGenerator.java
+===================================================================
+--- netlib-java.orig/src/org/netlib/generate/JavaGenerator.java
++++ netlib-java/src/org/netlib/generate/JavaGenerator.java
 @@ -51,6 +51,8 @@ import org.netlib.util.doubleW;
  import org.netlib.util.floatW;
  import org.netlib.util.intW;
@@ -40,9 +39,19 @@ index fda8e9d..15815de 100644
 +		URL url3 = new URL("file:///usr/share/java/jlapack-blas-0.8.jar");
 +		URL url4 = new URL("file:///usr/share/java/jlapack-lapack-0.8.jar");
 +		URL url5 = new URL("file:///usr/share/java/jlapack-xerbla-0.8.jar");
-+		URL url6 = new URL("file:///build/netlib-java-0.9.3/build/classes/");
++		URL url6 = new URL("file://" + new File(".").getAbsolutePath() + "/build/classes/");
 +
 +		URL [] classpath = { url1, url2, url3, url4, url5, url6 };
  		List<Class<?>> result = new ArrayList<Class<?>>();
  		System.out.println(Arrays.toString(classpath));
  		for (URL url : classpath) {
+@@ -700,6 +710,9 @@ class JavaGenerator {
+ 				// class path is a directory
+ 				File packageDirectory =
+ 						new File(file.getPath() + "/" + packagePath);
++				if(packageDirectory.listFiles() == null) {
++					throw new IllegalStateException("Could not find directory " + packageDirectory + " at " + packageDirectory.getAbsolutePath());
++				}
+ 				for (File f : packageDirectory.listFiles()) {
+ 					if (f.getPath().endsWith(".class")) {
+ 						String className =