Fix potential access issues when backporting

Backporting nest host/members is not supported and can therefore introduce access issue.
Running the access fixer if `-allowaccessmodification` is set solves this issue by setting appropriate visibility.

Author: daphnis.chevreton

base/src/main/java/proguard/backport/Backporter.java

@@ -314,6 +314,12 @@ public void execute(AppView appView) throws IOException
             appView.programClassPool.classesAccept(new ClassVersionSetter(targetClassVersion));
         }
 
+        // Backporting may introduce access issues, for example related to nest members/host.
+        if (configuration.allowAccessModification)
+        {
+            appView.programClassPool.classesAccept(new AccessFixer());
+        }
+
         logger.info("  Number of converted string concatenations:     {}", replacedStringConcatCounter.getCount());
         logger.info("  Number of converted lambda expressions:        {}", lambdaExpressionCounter.getCount());
         logger.info("  Number of converted static interface methods:  {}", staticInterfaceMethodCounter.getCount());

docs/md/manual/releasenotes.md

@@ -1,3 +1,9 @@
+## Version 7.4.2
+
+### Bugfixes
+
+- Fix potential access issues when backporting.
+
 ## Version 7.4.1
 
 ### Bugfixes