menu_displaylist: fold the no-entries fallback into one helper

Twenty-nine screens spelled the same six-line stanza inline - if
nothing was appended, append the no-entries row - in a counting
form and a result-discarding form. One helper replaces both, each
site now a single line; 142 lines gone net. Gated by the extended
dump: all 212 ctl sections and the build_list pass compare
byte-identical, the fallback rows included.

Author: libretroadmin