fix opening/saving audio files with non-ASCII char

s on Windows

this required making a wrapper...

src/engine/sfWrapper.h

@@ -0,0 +1,54 @@
+/**
+ * Furnace Tracker - multi-system chiptune tracker
+ * Copyright (C) 2021-2022 tildearrow and contributors
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+// sfWrapper.h: libsndfile FILE* wrapper to work around Windows issue with
+//              non-ASCII chars in file path
+//              I wanted to do this in sndfile directly, but it's a
+//              submodule...
+
+#ifndef _SFWRAPPER_H
+#define _SFWRAPPER_H
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <sndfile.h>
+#include "../ta-utils.h"
+
+class SFWrapper {
+  FILE* f;
+  size_t len;
+  SF_VIRTUAL_IO vio;
+  SNDFILE* sf;
+
+  public:
+    sf_count_t ioGetSize();
+    sf_count_t ioSeek(sf_count_t offset, int whence);
+    sf_count_t ioRead(void* ptr, sf_count_t count);
+    sf_count_t ioWrite(const void* ptr, sf_count_t count);
+    sf_count_t ioTell();
+
+    int doClose();
+    SNDFILE* doOpen(const char* path, int mode, SF_INFO* sfinfo);
+    SFWrapper():
+      f(NULL),
+      len(0),
+      sf(NULL) {}
+};
+
+#endif