Revert f8 behaviour, to run until next start of vblank, by re-adding a check that was removed as part of this commit (nw)

SHA-1: 56bd36c5ef
* Major refactoring of debugger core [Ryan Holtz]
* Eliminate globals/file statics
* Remove lots of stuff from global scope
* Use std::function for custom command registration
* Eliminate some trampolines
* Build fixes from Vas Crabb and balr0g

src/emu/debug/debugcpu.cpp

@@ -767,6 +767,7 @@ u64 debugger_cpu::read_opcode(address_space &space, offs_t address, int size)
 void debugger_cpu::on_vblank(screen_device &device, bool vblank_state)
 {
 	/* just set a global flag to be consumed later */
+	if (vblank_state)
 		m_vblank_occurred = true;
 }