Windows: Avoid segfault if memory except on boot.

Core/System.cpp

@@ -122,7 +122,8 @@ void UpdateUIState(GlobalUIState newState) {
 	// Never leave the EXIT state.
 	if (globalUIState != newState && globalUIState != UISTATE_EXIT) {
 		globalUIState = newState;
-		host->UpdateDisassembly();
+		if (host)
+			host->UpdateDisassembly();
 		const char *state = nullptr;
 		switch (globalUIState) {
 		case UISTATE_EXIT: state = "exit";  break;

Windows/Debugger/Debugger_MemoryDlg.cpp

@@ -131,9 +131,8 @@ void CMemoryDlg::searchBoxRedraw(std::vector<u32> results) {
 }
 
 
-void CMemoryDlg::NotifyMapLoaded()
-{
-	if (m_hDlg)
+void CMemoryDlg::NotifyMapLoaded() {
+	if (m_hDlg && g_symbolMap)
 		g_symbolMap->FillSymbolListBox(symListHdl, ST_DATA);
 	Update(); 
 }

Windows/EmuThread.cpp

@@ -263,6 +263,9 @@ void MainThreadFunc() {
 			if (!Core_IsActive())
 				UpdateUIState(UISTATE_MENU);
 			Core_Run(g_graphicsContext);
+			if (coreState == CORE_BOOT_ERROR) {
+				break;
+			}
 		}
 	}
 	Core_Stop();