fix(rla): Improve robustness for currupt files

Clean up seeking methodology to be more robust.

Fixes 5159

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

Author: lgritz

src/rla.imageio/rlainput.cpp

@@ -246,16 +246,18 @@ RLAInput::seek_subimage(int subimage, int miplevel)
         if (!read_header())
             return false;  // read_header always calls error()
         diff = subimage;
+        m_subimage = 0;
     }
     // forward scrolling -- skip subimages until we're at the right place
-    while (diff > 0 && m_rla.NextOffset != 0) {
+    while (diff > 0 && m_subimage < subimage && m_rla.NextOffset != 0) {
         if (!ioseek(m_rla.NextOffset)) {
             errorfmt("Could not seek to header offset. Corrupted file?");
             return false;
         }
         if (!read_header())
             return false;  // read_header always calls error()
         --diff;
+        ++m_subimage;
     }
     if (diff > 0 && m_rla.NextOffset == 0) {  // no more subimages to read
         errorfmt("Unknown subimage");
@@ -545,7 +547,7 @@ RLAInput::decode_channel_group(int first_channel, short num_channels,
         offset    = 0;
         pixelsize = m_spec.pixel_bytes(true);
         for (int i = 0; i < first_channel; ++i)
-            offset += m_spec.channelformats[i].size();
+            offset += m_spec.channelformat(i).size();
     }
 
     // Read the big-endian values into the buffer.

testsuite/rla/ref/out.txt

@@ -325,5 +325,8 @@ Full command line was:
 oiiotool ERROR: read : "src/crash-5152.rla": Read error: malformed RLE record
 Full command line was:
 > oiiotool src/crash-5152.rla -o crash6.exr
+oiiotool ERROR: read : "src/crash-5159.rla": Read error: couldn't read RLE data span
+Full command line was:
+> oiiotool src/crash-5159.rla -o crash7.exr
 Comparing "rlacrop.rla" and "ref/rlacrop.rla"
 PASS

testsuite/rla/run.py

@@ -24,5 +24,6 @@
 command += oiiotool("src/crash-3951.rla -o crash4.exr", failureok = True)
 command += oiiotool("src/crash-1.rla -o crash5.exr", failureok = True)
 command += oiiotool("src/crash-5152.rla -o crash6.exr", failureok = True)
+command += oiiotool("src/crash-5159.rla -o crash7.exr", failureok = True)
 
 outputs = [ "rlacrop.rla", 'out.txt' ]