Multimedia: Fix compiler warning warning C4723: potential divide by 0

cl.exe 19.35.32217.1 for x64 emits warning C4723: potential divide by 0
in RelWithDebInfo build of QtMultimedia.dll. The reason is likely that
the compiler can not rule out that the QAudioFormat::bytesPerSample
returns a different value from the point of check to the point of read.

Change-Id: Ifcc2db06310c94a7b90514f54d4d9e9c94c63072
Reviewed-by: Lars Knoll <lars@knoll.priv.no>
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
(cherry picked from commit dda06373eba84999a89e539035860fc45f2fa5f5)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/src/multimedia/audio/qwavedecoder.cpp b/src/multimedia/audio/qwavedecoder.cpp
index a61d49b06..df5ee32cc 100644
--- a/src/multimedia/audio/qwavedecoder.cpp
+++ b/src/multimedia/audio/qwavedecoder.cpp
@@ -139,7 +139,8 @@ qint64 QWaveDecoder::headerLength()
 
 qint64 QWaveDecoder::readData(char *data, qint64 maxlen)
 {
-    if (!haveFormat || format.bytesPerSample() == 0)
+    const int bytesPerSample = format.bytesPerSample();
+    if (!haveFormat || bytesPerSample == 0)
         return 0;
 
     if (bps == 24) {
@@ -163,15 +164,15 @@ qint64 QWaveDecoder::readData(char *data, qint64 maxlen)
         return l;
     }
 
-    qint64 nSamples = maxlen / format.bytesPerSample();
-    maxlen = nSamples * format.bytesPerSample();
+    qint64 nSamples = maxlen / bytesPerSample;
+    maxlen = nSamples * bytesPerSample;
     int read = device->read(data, maxlen);
 
     if (!byteSwap || format.bytesPerFrame() == 1)
         return read;
 
-    nSamples = read / format.bytesPerSample();
-    switch (format.bytesPerSample()) {
+    nSamples = read / bytesPerSample;
+    switch (bytesPerSample) {
     case 2:
         bswap2(data, nSamples);
         break;