[zeditor] Freeze when selecting MIDI

onMidis() in zquest.cpp runs when clicking MIDIs in step 1. Then the call to do_zqdialog immediately following the call to go() creates the "Select music" window.

The button labels on the Select music window come from the selectmidi_dlg array in zquest.cpp

This while loop appears to be degenerating into an infinite loop:

        while(update_dialog(p))
        {
            custom_vsync();
            //      text_mode(vc(1));
            textprintf_ex(screen,get_zc_font(font_lfont_l),editmidi_dlg[0].x+int32_t(193*1.5),editmidi_dlg[0].y+int32_t(58*1.5),jwin_pal[jcBOXFG],jwin_pal[jcBOX],"%-5ld",midi_pos);
        }

control never seems to flow down to the rest of edit_tune(int32_t i), the next non-blank line of which is:

        ret = shutdown_dialog(p);

Commenting out that while loop doesn't fix it because then the do while(ret<26&&ret!=0); loop degenerates into an infinite loop with ret == -1

Uncommenting text_mode(vc(1)); doesn't help break out of the while(update_dialog(p)) loop.

v2.50 Build 28 correctly brings up the "MIDI Specs" window when clicking the "Edit" button.