PNG: fix reading 16-bit interlaced images (on little-endian machines)

Fixes https://lists.osgeo.org/pipermail/gdal-dev/2024-December/059989.html

autotest/gdrivers/png.py

@@ -471,3 +471,13 @@ def test_png_copy_mdd():
     ds = None
 
     gdal.Unlink(filename)
+
+
+###############################################################################
+# Read test of 16-bit interlaced
+
+
+def test_png_read_interlace_16_bit():
+
+    ds = gdal.Open("data/png/uint16_interlaced.png")
+    assert ds.GetRasterBand(1).Checksum() == 4672

frmts/png/pngdataset.cpp

@@ -1405,6 +1405,21 @@ CPLErr PNGDataset::LoadInterlacedChunk(int iLine)
 
     bool bRet = safe_png_read_image(hPNG, png_rows, sSetJmpContext);
 
+    // Do swap on LSB machines. 16-bit PNG data is stored in MSB format.
+#ifdef CPL_LSB
+    if (bRet && nBitDepth == 16)
+    {
+        for (int i = 0; i < GetRasterYSize(); i++)
+        {
+            if (i >= nBufferStartLine && i < nBufferStartLine + nBufferLines)
+            {
+                GDALSwapWords(png_rows[i], 2,
+                              GetRasterXSize() * GetRasterCount(), 2);
+            }
+        }
+    }
+#endif
+
     CPLFree(png_rows);
     CPLFree(dummy_row);
     if (!bRet)