Fix QWebpHandler::canRead() to take animation frame count into account

Task-number: QTBUG-61641
Change-Id: I24a139cc75141a588f2ed2558da85cd2f8391af9
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

src/plugins/imageformats/webp/qwebphandler.cpp

@@ -74,6 +74,10 @@ bool QWebpHandler::canRead() const
 
     if (m_scanState != ScanError) {
         setFormat(QByteArrayLiteral("webp"));
+
+        if (m_features.has_animation && m_iter.frame_num >= m_frameCount)
+            return false;
+
         return true;
     }
     return false;

tests/auto/webp/tst_qwebp.cpp

@@ -127,6 +127,7 @@ void tst_qwebp::readAnimation()
     }
 
     QVERIFY(reader.read().isNull());
+    QCOMPARE(reader.canRead(), !reader.supportsAnimation());
 }
 
 void tst_qwebp::writeImage_data()