handle source repos with broken links to gradle files

https://github.com/kiwibrowser/src has a build.gradle that is a broken link:

$ ls -l build/com.google.ar.core.examples.java.helloar/third_party/android_sdk/public/extras/android/support/v4/src/build.gradle
lrwxrwxrwx 1 hans hans 92 Mai 11 17:29 build/com.google.ar.core.examples.java.helloar/third_party/android_sdk/public/extras/android/support/v4/src/build.gradle -> ../../../../../../../../../.cipd/pkgs/80/_current/extras/android/support/v4/src/build.gradle

.issuebot.py

@@ -264,12 +264,13 @@ for issue in rfp.issues.list(state='opened',order_by='updated_at',per_page=250):
                         if f.endswith('.gradle') or f.endswith('.gradle.kts'):
                             labels.add('gradle')
                             path = os.path.join(root, f)
-                            with open(path, errors='surrogateescape') as fp:
-                                data = fp.read()
-                            for url in HTTP_GRADLE_PATTERN.findall(data):
-                                print('Found plain HTTP URL for gradle repository:\n%s\n%s'
-                                      % (path, url))
-                                insecure_repositories.add(url)
+                            if os.path.exists(path):
+                                with open(path, errors='surrogateescape') as fp:
+                                    data = fp.read()
+                                for url in HTTP_GRADLE_PATTERN.findall(data):
+                                    print('Found plain HTTP URL for gradle repository:\n%s\n%s'
+                                          % (path, url))
+                                    insecure_repositories.add(url)
                         elif f.endswith('.java'):
                             labels.add('java')
                         elif f.endswith('.kt'):