Reinstate escape hatch for findResource()

Reinstate the defensive call of super.findResource() in
LaunchedURLClassLoader.

Closes gh-5650
See gh-486

spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/LaunchedURLClassLoader.java

@@ -49,9 +49,14 @@ public class LaunchedURLClassLoader extends URLClassLoader {
 	@Override
 	public URL findResource(String name) {
 		Handler.setUseFastConnectionExceptions(true);
+		try {
 			try {
 				return super.findResource(name);
 			}
+			catch (IllegalArgumentException ex) {
+				return null;
+			}
+		}
 		finally {
 			Handler.setUseFastConnectionExceptions(false);
 		}