Merge pull request #1799 from SuperKael/release-upload-fix

Only try to strip upload url 'helpful garbage' if it is present

src/main/java/org/kohsuke/github/GHRelease.java

@@ -274,7 +274,10 @@ public GHAsset uploadAsset(String filename, InputStream stream, String contentTy
         Requester builder = owner.root().createRequest().method("POST");
         String url = getUploadUrl();
         // strip the helpful garbage from the url
-        url = url.substring(0, url.indexOf('{'));
+        int endIndex = url.indexOf('{');
+        if (endIndex != -1) {
+            url = url.substring(0, endIndex);
+        }
         url += "?name=" + URLEncoder.encode(filename, "UTF-8");
         return builder.contentType(contentType).with(stream).withUrlPath(url).fetch(GHAsset.class).wrap(this);
     }