fix(raw) check for nullptr in raw input plugin (AcademySoftwareFoundation#4448)

This adds a null pointer check in the raw input plugin when the user
requested raw bayer data for a file format which doesn't have it. With
this fix OIIO shows an error instead of crashing in such case.

This fixes the issue mentioned in the comments of AcademySoftwareFoundation#4361. The title issue
of AcademySoftwareFoundation#4361 has been resolved in LibRaw 0.22.0, so we can close that issue,
I guess.

This also fixes the crash on 5 out of 6 examples in AcademySoftwareFoundation#3115. The last one
is unrelated, and I don't have a good fix for that at this time (crash
due to the raw buffer having half resolution, with the pixel aspect
ratio of 0.5). Perhaps we could create a separate issue and close AcademySoftwareFoundation#3115.

I have not added any tests for this change specifically, as it is fairly
trivial.
I have started working on a more comprehensive test suite for the raw
plugin / rawtoaces, but it's not ready yet, and I'm not sure where it
should live at this stage.

Signed-off-by: Anton Dukhovnikov <[email protected]>

Author: antond-weta

src/raw.imageio/rawinput.cpp

@@ -1527,6 +1527,13 @@ RawInput::read_native_scanline(int subimage, int miplevel, int y, int /*z*/,
     if (!m_process) {
         // The user has selected not to apply any debayering.
 
+        if (m_processor->imgdata.rawdata.raw_image == nullptr) {
+            errorfmt(
+                "Raw undebayered data is not available for this file \"{}\"",
+                m_filename);
+            return false;
+        }
+
         // The raw_image buffer might contain junk pixels that are usually trimmed off
         // we must index into the raw buffer, taking these into account
         auto& sizes        = m_processor->imgdata.sizes;