Assert in QBmpHandler's read_dib_body() when loading palette based BMP images

When trying to load palette based or monochrome bmp images, Qt asserts. I believe this regression has been introduced by a237c2cacec31e1aef00ff4e0b5707efc52d9b31 It worked fine in Qt 4.7

Stack trace:

0 ?? /lib/ld-linux.so.2 0 0x110832
1 raise /lib/i386-linux-gnu/libc.so.6 0 0x12ade71
2 abort /lib/i386-linux-gnu/libc.so.6 0 0x12b134e
3 qt_message_output qglobal.cpp 2252 0xe62bbb
4 qt_message qglobal.cpp 2298 0xe62d5d
5 qFatal qglobal.cpp 2481 0xe63189
6 qt_assert qglobal.cpp 1999 0xe62760
7 read_dib_body qbmphandler.cpp 263 0x3fae8e
8 QBmpHandler::read qbmphandler.cpp 772 0x3fcde3
9 QImageReader::read qimagereader.cpp 1205 0x3c8ee4
10 QImageReader::read qimagereader.cpp 1155 0x3c8b58
11 QImage::load qimage.cpp 5087 0x3ba361

I attached a few bmp images with different formtas which cause the assert in debug builds.

Note: The assert does obviously affect the release mode. Interestingly, in release mode, the image loading succeeds.