fix(render48k): chunk-scan WAV loader — hdr[40] is not data size when bext/junk present

dsp/render48k.cpp

@@ -26,7 +26,21 @@ static bool load_wav(const char* path, std::vector<float>& out, int& sr) {
     sr = *(int*)(hdr + 24);
     int ch = *(short*)(hdr + 22);
     int bits = *(short*)(hdr + 34);
-    int data = *(int*)(hdr + 40);
+    // scan chunks to find data chunk size (hdr[40] may be bext/junk size)
+    int data = 0;
+    int64_t pos = 12;
+    fseek(f, 12, SEEK_SET);
+    while (pos < 32 * 1024 * 1024) {
+        char cid[4]; int csize;
+        if (fread(cid, 1, 4, f) < 4 || fread(&csize, 4, 1, f) < 1) break;
+        pos += 8;
+        if (memcmp(cid, "data", 4) == 0) { data = csize; break; }
+        pos += csize;
+        int skip = csize;
+        if (csize % 2) skip++;  // odd chunk size padded
+        fseek(f, skip, SEEK_CUR);
+    }
+    if (!data) { fclose(f); return false; }
     int n = data / (ch * (bits / 8));
     g_in_ch = ch;
     out.resize(n);