Bug 14078: converting from ISO5426 is not complete

Bug 14078: converting from ISO5426 is not complete

Conversion of MARC from ISO5426 is defined in C4::Charset::char_decode5426().
Each character or combined characters conversion is defined in a map.

This patch changes some odd actual conversions.

In char_decode5426(), only characters between 0xC0 and 0xDF will be used for combining with following charater :
  ($char >= 0xC0 && $char <= 0xDF)
So conversion like "$chars{0x81d1}=0x00b0" will never be used.
Rules for "h with breve below" use combining with 0xf9 but looks like the correct caracter is 0xd5.

See http://www.gymel.com/charsets/MAB2.html

Signed-off-by: Frederic Demians <f.demians@tamil.fr>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>