Merge branch 'bak2bak' into 'next'

Autobackup old gamedatas (resolves #1031)

Closes #1031

See merge request STJr/SRB2!2030

src/g_game.c

@@ -4386,6 +4386,17 @@ void G_LoadGameData(gamedata_t *data)
 		{
 			goto datacorrupt;
 		}
+
+		// make a backup of the old data
+		char currentfilename[64];
+		char backupfilename[69];
+		char bak[5];
+
+		strcpy(bak, ".bak");
+		strcpy(currentfilename, gamedatafilename);
+		STRBUFCPY(backupfilename, strcat(currentfilename, bak));
+
+		FIL_WriteFile(va(pandf, srb2home, backupfilename), savebuffer, length);
 	}
 	else
 #endif