QImageWriter: add a forgotten #ifndef QT_NO_IMAGEFORMAT_BPM

The equivalent code in qimagereader.cpp has this, so add here, too.

Change-Id: I0313727f009db5cb00ee9ce0540ba2674da49ccd
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/gui/image/qimagewriter.cpp

@@ -772,7 +772,9 @@ QList<QByteArray> QImageWriter::supportedImageFormats()
 QList<QByteArray> QImageWriter::supportedMimeTypes()
 {
     QSet<QByteArray> mimeTypes;
+#ifndef QT_NO_IMAGEFORMAT_BMP
     mimeTypes << "image/bmp";
+#endif
 #ifndef QT_NO_IMAGEFORMAT_PPM
     mimeTypes << "image/x-portable-bitmap";
     mimeTypes << "image/x-portable-graymap";