Fix version guessing for paths without extensions, or extensions other then .jar (#34)

Author: heisluft

src/main/java/cpw/mods/jarhandling/JarMetadata.java

@@ -75,8 +75,12 @@ static SimpleJarMetadata fromFileName(final Path path, final Set<String> pkgs, f
         }
 
         // fallback parsing
-        var fn = path.getFileName().toString();
-        fn = fn.substring(0, fn.length()-4); // no .jar extension
+        var fn = path.getFileName().toString();     
+        var lastDot = fn.lastIndexOf('.');
+        if (lastDot > 0) {
+            fn = fn.substring(0, lastDot); // strip extension if possible
+        }
+       
         var mat = DASH_VERSION.matcher(fn);
         if (mat.find()) {
             var ver = ModuleDescriptor.Version.parse(fn.substring(mat.start() + 1)).toString();