[PATCH] Fix crash in qppmhandler for certain malformed image files

[PATCH] Fix crash in qppmhandler for certain malformed image files

The ppm format specifies that the maximum color value field must be
less than 65536. The handler did not enforce this, leading to
potentional overflow when the value was used in 16 bits context.

Task-number: QTBUG-69449
Change-Id: Iea7a7e0f8953ec1ea8571e215687d12a9d77e11c
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Gbp-Pq: Name CVE-2018-19872.patch