savestate undo 2.0rc1: error message if undo fails (nothing to be undone) & fixed/oops: dont undo the last savestate

src/burner/state.cpp

@@ -284,6 +284,15 @@ INT32 BurnStateSaveEmbed(FILE* fp, INT32 nOffset, INT32 bAll)
 	return nDefLen;
 }
 
+#ifdef _WIN32
+int FileExists(const TCHAR *fileName)
+{
+    DWORD dwAttrib = GetFileAttributes(fileName);
+    return (dwAttrib != INVALID_FILE_ATTRIBUTES &&
+            !(dwAttrib & FILE_ATTRIBUTE_DIRECTORY));
+}
+#endif
+
 #define MAX_STATEBACKUPS 10
 // SaveState Undo - restores the last savestate backup file. Windows-only at the moment.
 INT32 BurnStateUNDO(TCHAR* szName)
@@ -296,26 +305,33 @@ INT32 BurnStateUNDO(TCHAR* szName)
          derp.fs.backup2 -> derpfs.backup1
          derp.fs.backup3 -> derpfs.backup2
          */
+    INT32 cantundo = 0;
 
     for (INT32 i = 0; i <= MAX_STATEBACKUPS; i++) {
             TCHAR szBackupNameTo[1024] = _T("");
             TCHAR szBackupNameFrom[1024] = _T("");
+            TCHAR szBackupNamePrev[1024] = _T("");
 
             if (i == 0) {
                 _stprintf(szBackupNameTo, _T("%s.UNDO"), szName);// game.fs -> game.fs.UNDO
-                DeleteFileW(szBackupNameTo);
-                MoveFileW(szName, szBackupNameTo);
+                _stprintf(szBackupNamePrev, _T("%s.backup0"), szName);
+                if (FileExists(szName) && FileExists(szBackupNamePrev)) {
+                    DeleteFileW(szBackupNameTo);
+                    MoveFileW(szName, szBackupNameTo);
+                } else {
+                    cantundo = 1;
+                }
 
                 _stprintf(szBackupNameTo, _T("%s"), szName);// game.fs
             } else {
                 _stprintf(szBackupNameTo, _T("%s.backup%d"), szName, i - 1); //game.fs.backup0
             }
             _stprintf(szBackupNameFrom, _T("%s.backup%d"), szName, i); //game.fs.backup1
-            //bprintf(0, _T("%s -> %s\n"), szBackupNameFrom, szBackupNameTo);
+            //bprintf(0, _T("%d: %s -> %s\n"), i, szBackupNameFrom, szBackupNameTo);
             MoveFileW(szBackupNameFrom, szBackupNameTo);
     }
 #endif
-    return 0;
+    return cantundo;
 }
 
 // State save

src/burner/win32/burner_win32.h

@@ -373,7 +373,7 @@ int InpcCreate();
 extern int bDrvSaveAll;
 int StatedAuto(int bSave);
 int StatedLoad(int nSlot);
-void StatedUNDO(int nSlot);
+int StatedUNDO(int nSlot);
 int StatedSave(int nSlot);
 
 // numdial.cpp

src/burner/win32/scrn.cpp

@@ -1080,16 +1080,18 @@ static void OnCommand(HWND /*hDlg*/, int id, HWND /*hwndCtl*/, UINT codeNotify)
 			PausedRedraw();
 			break;
 		}
-		case MENU_STATE_UNDO: {
+		case MENU_STATE_UNDO:
 			if (bDrvOkay) {
 				TCHAR szString[256] = _T("state undo");
-
-				StatedUNDO(nSavestateSlot);
-				VidSNewShortMsg(szString);
-				PausedRedraw();
+				TCHAR szStringFailed[256] = _T("state: nothing to undo");
+				if (!StatedUNDO(nSavestateSlot)) {
+					VidSNewShortMsg(szString);
+				} else {
+					VidSNewShortMsg(szStringFailed);
 				}
-			break;
+				PausedRedraw();
 			}
+			break;
 		case MENU_STATE_LOAD_SLOT:
 			if (bDrvOkay && !kNetGame) {
 				if (StatedLoad(nSavestateSlot) == 0) {

src/burner/win32/stated.cpp

@@ -45,12 +45,13 @@ static void CreateStateName(int nSlot)
 	_stprintf(szChoice, _T("./savestates/%s slot %02x.fs"), BurnDrvGetText(DRV_NAME), nSlot);
 }
 
-void StatedUNDO(int nSlot)
+int StatedUNDO(int nSlot)
 {
-    if (nSlot) {
-        CreateStateName(nSlot);
-        BurnStateUNDO(szChoice);
-    }
+	if (nSlot) {
+		CreateStateName(nSlot);
+		return BurnStateUNDO(szChoice);
+	}
+	return 1;
 }
 
 int StatedLoad(int nSlot)