Examples: fix a couple of nodiscard warnings from QFile::open

In one case, the code simply checked for isOpen afterwards; refactor
it to use QFile::open's result. In another case, a file was opened
from the resource system, so add a check.

Pick-to: 6.8
Change-Id: I5f4c22dd5ce678f15c9c1609c4228d50a2b32a1d
Reviewed-by: Thiago Macieira <[email protected]>
(cherry picked from commit eeead68)
Reviewed-by: Qt Cherry-pick Bot <[email protected]>

Author: dangelog

examples/corelib/serialization/convert/main.cpp

@@ -23,12 +23,14 @@ static const Converter *prepareConverter(QString format, Converter::Direction di
         : QIODevice::ReadOnly;
     const char *dirn = out ? "output" : "input";
 
+    bool isOpen;
+
     if (stream->fileName().isEmpty())
-        stream->open(out ? stdout : stdin, mode);
+        isOpen = stream->open(out ? stdout : stdin, mode);
     else
-        stream->open(mode);
+        isOpen = stream->open(mode);
 
-    if (!stream->isOpen()) {
+    if (!isOpen) {
         qFatal("Could not open \"%s\" for %s: %s",
                qPrintable(stream->fileName()), dirn, qPrintable(stream->errorString()));
     } else if (format == "auto"_L1) {

examples/widgets/draganddrop/draggabletext/dragwidget.cpp

@@ -20,7 +20,12 @@ DragWidget::DragWidget(QWidget *parent)
     : QWidget(parent)
 {
     QFile dictionaryFile(QStringLiteral(":/dictionary/words.txt"));
-    dictionaryFile.open(QIODevice::ReadOnly);
+    if (!dictionaryFile.open(QIODevice::ReadOnly)) {
+        // This would be a build problem, as the dictionary is in the
+        // resource system.
+        qFatal("Could not open the dictionary file: %s",
+               qPrintable(dictionaryFile.errorString()));
+    }
     QTextStream inputStream(&dictionaryFile);
 
     int x = 5;