QMovie: fix quadratic behavior

Repeatedly calling QList::erase(it) (via QMutableListIterator::remove())
results in quadratic runtime.

Use std::remove_if, which does exactly what the old code tried to do,
except in linear time.

Change-Id: I682e5e05f04953ae1c8788e5d66335241de39fee
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/gui/image/qmovie.cpp

@@ -965,14 +965,16 @@ void QMovie::setScaledSize(const QSize &size)
 QList<QByteArray> QMovie::supportedFormats()
 {
     QList<QByteArray> list = QImageReader::supportedImageFormats();
-    QMutableListIterator<QByteArray> it(list);
+
     QBuffer buffer;
     buffer.open(QIODevice::ReadOnly);
-    while (it.hasNext()) {
-        QImageReader reader(&buffer, it.next());
-        if (!reader.supportsAnimation())
-            it.remove();
-    }
+
+    const auto doesntSupportAnimation =
+            [&buffer](const QByteArray &format) {
+                return !QImageReader(&buffer, format).supportsAnimation();
+            };
+
+    list.erase(std::remove_if(list.begin(), list.end(), doesntSupportAnimation), list.end());
     return list;
 }