[mpeg2enc] display_horizontal_size must be in range 0...16383

When using mpeg2enc with option "-f 13" (ATSC 1080i) it aborts with

[mpeg2enc] display_horizontal_size must be in range 0...16383

This is because of a bug in encoderparams.cc. There are some special rules for setting display_horizontal_size and display_vertical_size for certain formats. In the case of MPEG_FORMAT_ATSC1080i the display_vertical_size is fixed set to 1080, because the input image is 1088 in size (must be a multiple of 16). The display_horizontal_size is not set in this case and it remains uninitialized because the default case is not executed (which sets also display_horizontal_size).

There are 2 possible solutions:

1. set the display_horizontal_size to a fixed value of 1920 in the case of MPEG_FORMAT_ATSC1080i.

2. move the code which sets these variables in the default case just before the case statement.