QXpmHandler: actually limit characters-per-pixel to four

The following code assumed, and all comments indicated, that the cpp
variable was limited to a max of 4. Yet, as coded, cpp could be five,
in which case the XPM would be corrupt, as the header suggested five
characters-per-pixel while the data was formatted in only four.

Add a warning and error out when we encounter this situation.

[ChangeLog][QtGui][QImage] Instead of writing a corrupt file, rejects
to write XPM files with more than 64^4 colors (more than four
characters per pixel) now.

Pick-to: 6.2 6.1 5.15 5.12
Change-Id: I458873cf7d179ab2e2dacd4c17dc837d640591a9
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

0 files changed, 0 insertions, 0 deletions