QIODevice: rework validation policy for read() functions

- avoid calls to private and virtual functions, if the device is not
  open;
- avoid repetitive checks in loops;
- add missing checks in readLine() overloads;
- remove check against unsuccessful resize().

Change-Id: I973d5931163b25db1c09c7c3b66f29ea90bb1b29
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

1 files changed, 3 insertions, 0 deletions

diff --git a/tests/auto/corelib/io/qiodevice/tst_qiodevice.cpp b/tests/auto/corelib/io/qiodevice/tst_qiodevice.cpp
index 0a4e3aefea..a754984d03 100644
--- a/tests/auto/corelib/io/qiodevice/tst_qiodevice.cpp
+++ b/tests/auto/corelib/io/qiodevice/tst_qiodevice.cpp
@@ -407,6 +407,9 @@ void tst_QIODevice::readLine()
     QVERIFY(buffer.open(QIODevice::ReadWrite));
     QVERIFY(buffer.canReadLine());
 
+    QTest::ignoreMessage(QtWarningMsg, "QIODevice::readLine (QBuffer): Called with maxSize < 2");
+    QCOMPARE(buffer.readLine(nullptr, 0), qint64(-1));
+
     int linelen = data.indexOf('\n') + 1;
     QByteArray line;
     line.reserve(linelen + 100);