fix(psd): Prevent simultaneous psd thumbnail reads from clashing (Aca…

…demySoftwareFoundation#3877)

When reading a PSD file, if it contains a thumbnail, we read it from the
in-memory blob with a combination of an IOMemReader and an ImageBuf.
But... we always named it "thumbnail.jpg" without considering that
multiple simultaneous PSD files reading identically named images (but
which are in fact different) could cause a weird kind of clashing in any
underlying use of ImageCache!

The simple fix is to use ordinary ImageInput approach to reading the
thumbnail from the IOMemReader, but just store it in the ImageBuf.

Fixes AcademySoftwareFoundation#3824

Signed-off-by: Larry Gritz <lg@larrygritz.com>

src/psd.imageio/psdinput.cpp

@@ -1322,9 +1322,27 @@ PSDInput::load_resource_thumbnail(uint32_t length, bool isBGR)
     if (!ioread(&jpeg_data[0], jpeg_length))
         return false;
 
+    // Create an IOMemReader that references the thumbnail JPEG blob and read
+    // it with an ImageInput, into the memory owned by an ImageBuf.
     Filesystem::IOMemReader thumbblob(jpeg_data.data(), jpeg_length);
-    m_thumbnail = ImageBuf("thumbnail.jpg", 0, 0, nullptr, nullptr, &thumbblob);
-    m_thumbnail.read(0, 0, true);
+    m_thumbnail.clear();
+    auto imgin = ImageInput::open("thumbnail.jpg", nullptr, &thumbblob);
+    if (imgin) {
+        ImageSpec spec = imgin->spec(0);
+        m_thumbnail.reset(spec, InitializePixels::No);
+        ok = imgin->read_image(0, 0, 0, m_thumbnail.spec().nchannels,
+                               m_thumbnail.spec().format,
+                               m_thumbnail.localpixels());
+        imgin.reset();
+    } else {
+        errorfmt("Failed to open thumbnail");
+        return false;
+    }
+    if (!ok) {
+        errorfmt("Failed to read thumbnail: {}", m_thumbnail.geterror());
+        m_thumbnail.clear();
+        return false;
+    }
 
     // Set these attributes for the merged composite only (subimage 0)
     composite_attribute("thumbnail_width", (int)m_thumbnail.spec().width);