The server sided handling of the display control channel currently
treats the physical monitor size values as obligatory values.
When the physical monitor size is invalid according to the
documentation, it is supposed to be ignored.
However, this is currently not done, leading to an abort of the display
control channel handling, when using Remmina, as Remmina does not submit
physical-monitor- widths and -heights.
Fix this issue by sanitizing the physical monitor size values, instead
of handling them as obligatory values, where both the physical with and
the physical height must be constrained to the values in the
documentation.