fix(main): continue to next icon candidate if nativeImage is empty

If a Linux icon path exists (fs.existsSync) but the file is unreadable
or corrupt, nativeImage.createFromPath() returns an empty NativeImage.
Returning undefined immediately skips all remaining fallback candidates.
Use continue so the loop advances to the next path instead.

Addresses: #615 (review)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: nerdCopter

main.js

@@ -75,7 +75,10 @@ function getWindowIconPath() {
       // and packaged (.deb) modes.
       if (process.platform === 'linux') {
         const img = nativeImage.createFromPath(iconPath);
-        return img.isEmpty() ? undefined : img;
+        if (!img.isEmpty()) {
+          return img;
+        }
+        continue;
       }
       return iconPath;
     }