Fix opcode table over-read crash on Windows

m68ki_build_opcode_table() scans past the end of the handler table
because the first while loop expects mask 0xff00 as a sentinel, but
m68kmake never generates entries with that mask. Add a zero-terminator
guard so the loop stops at the end of the table.

On Linux/macOS the over-read lands in zero-filled BSS and happens to
work. On Windows the read crosses into unmapped memory and crashes
with ACCESS_VIOLATION.

Author: tbdye

src/musashi/m68k_in.c

@@ -182,7 +182,7 @@ void m68ki_build_opcode_table(void)
 	}
 
 	ostruct = m68k_opcode_handler_table;
-	while(ostruct->mask != 0xff00)
+	while(ostruct->mask != 0xff00 && ostruct->mask != 0)
 	{
 		for(i = 0;i < 0x10000;i++)
 		{