fix: GameService.load() NPE on null bundleFile + ZipService test path

- GameService.load(): null-check bundleFile before resolving path
  (Path.resolve(null) throws NullPointerException)
- ZipServiceTest: pass absolute exePath to createBundle (relativize
  requires both paths to be absolute or both relative)

src/main/java/org/dostalgia/GameService.java

@@ -77,10 +77,13 @@ public class GameService implements GameStore {
         );
         // Detect bundle size
         try {
-            Path bundlePath = gamesDir.resolve(game.getBundleFile());
+            String bf = game.getBundleFile();
+            if (bf != null) {
+                Path bundlePath = gamesDir.resolve(bf);
                 if (Files.exists(bundlePath)) {
                     game.setBundleSize(Files.size(bundlePath));
                 }
+            }
         } catch (IOException ignored) {}
         return game;
     }

src/test/java/org/dostalgia/ZipServiceTest.java

@@ -154,7 +154,7 @@ class ZipServiceTest {
 
         Path bundlePath = dir.resolve("output.jsdos");
 
-        zip.createBundle(extractDir, "game.exe", List.of(), bundlePath);
+        zip.createBundle(extractDir, extractDir.resolve("game.exe").toString(), List.of(), bundlePath);
 
         assertTrue(Files.exists(bundlePath));
         assertTrue(Files.size(bundlePath) > 0);
@@ -193,7 +193,7 @@ class ZipServiceTest {
 
         Path bundlePath = dir.resolve("output.jsdos");
 
-        zip.createBundle(extractDir, "game.exe", List.of(), bundlePath);
+        zip.createBundle(extractDir, extractDir.resolve("game.exe").toString(), List.of(), bundlePath);
 
         try (ZipInputStream zis = new ZipInputStream(Files.newInputStream(bundlePath))) {
             ZipEntry entry;