Fix for WAI behavior (Fantavision)

[digarok]

From https://groups.google.com/forum/#!topic/comp.sys.apple2/NWjJ1_ytewQ
(Thanks fatdog)

Kent Dickey writes:
Fantavision hangs when it starts on KEGS-based emulators (which includes
GSport and GSplus) due to a bug in the way KEGS handles the WAI instruction.
Fantavision masks interrupts with SEI, sets a SHR line interrupt, and then
does a WAI instruction. This hangs KEGS since it expects an actual interrupt
to end the WAI, but there won't be one since interrupts are masked. I never
realized this was a valid WAI use case.

The fix is easy. In instable.h, change:

instcb_SYM              /*  WAI */
        g_wait_pending = 1;
        CYCLES_FINISH

(There may be some stale #ifdef ASM code, just ignore that) to:

instcb_SYM              /*  WAI */
        if(g_irq_pending) {
                g_wait_pending = 0;
                INC_KPC_1;
        } else {
                g_wait_pending = 1;
        }