[gimp] plug-ins: fix reading of FLI files where the filesize is off-by-on

[Jacob Boerema <jboerema src gnome org>]

commit 980e604880785865aea41716af83e4268ecc3ecf
Author: Jacob Boerema <jgboerema gmail com>
Date:   Mon May 16 11:21:57 2022 -0400

    plug-ins: fix reading of FLI files where the filesize is off-by-on

 plug-ins/file-fli/fli.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)
---
diff --git a/plug-ins/file-fli/fli.c b/plug-ins/file-fli/fli.c
index 7343817781..88ae239439 100644
--- a/plug-ins/file-fli/fli.c
+++ b/plug-ins/file-fli/fli.c
@@ -197,9 +197,15 @@ fli_read_header (FILE          *f,
 
 if (actual_size != fli_header->filesize && actual_size >= 0)
   {
-    g_warning (_("Incorrect file size in header: %u, should be: %u."),
-               fli_header->filesize, (guint) actual_size);
-    fli_header->filesize = actual_size;
+    /* Older versions of GIMP or other apps may incorrectly finish chunks on
+     * an odd length, but write filesize as if that last byte was written.
+     * Don't fail on off-by-one file size. */
+    if (actual_size + 1 != fli_header->filesize)
+      {
+        g_warning (_("Incorrect file size in header: %u, should be: %u."),
+                   fli_header->filesize, (guint) actual_size);
+        fli_header->filesize = actual_size;
+      }
   }
 
 if (fli_header->frames == 0)
@@ -341,7 +347,7 @@ fli_read_frame (FILE          *f,
             }
           g_debug ("Chunk offset: %u, chunk size: %u, chunk type: %u",
                    (guint) chunkpos, chunk.size, chunk.magic);
-          if (chunkpos + chunk.size >= fli_header->filesize)
+          if (chunkpos + chunk.size > fli_header->filesize)
             {
               g_set_error (error, G_FILE_ERROR, G_FILE_ERROR_FAILED,
                            _("Invalid chunk size points past end of file!"));