QFile::rename: fix the error message if renaming a file by copy fails

The QFile out variable cannot be open because if out.open() succeeded,
we could never reach this line. Instead, we want to capture *why* either
the source or the destination failed to open.

Task-number: QTBUG-66445
Change-Id: I940917d6763842499b18fffd15142f231bf34a47
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@qt.io>

src/corelib/io/qfile.cpp

@@ -676,8 +676,11 @@ QFile::rename(const QString &newName)
                 return !error;
             }
             close();
+            d->setError(QFile::RenameError,
+                        tr("Cannot open destination file: %1").arg(out.errorString()));
+        } else {
+            d->setError(QFile::RenameError, errorString());
         }
-        d->setError(QFile::RenameError, out.isOpen() ? errorString() : out.errorString());
     }
     return false;
 }