Update implementation to only update fixed entries

When a partial reconstruction happens, only update the fixed entries. If
it is a complete reconstruction, can copy full array blindly.

Signed-off-by: Kimball Thurston <kdt3rd@gmail.com>

Author: kdt3rd

src/lib/OpenEXRCore/chunk.c

@@ -424,7 +424,7 @@ reconstruct_chunk_table (
     uint64_t              offset_start, chunk_start, max_offset;
     uint64_t*             curctable;
     exr_const_priv_part_t curpart = NULL;
-    int                   found_ci, computed_ci, partnum = 0, lastreconstruct = -1;
+    int                   found_ci, computed_ci, partnum = 0;
     size_t                chunkbytes;
 
     curpart      = ctxt->parts[ctxt->num_parts - 1];
@@ -486,18 +486,24 @@ reconstruct_chunk_table (
             chunk_start = 0;
             if (firstfailrv == EXR_ERR_SUCCESS) firstfailrv = rv;
         }
-        else
-        {
-            lastreconstruct = ci;
-        }
 
         if (found_ci >= 0 && found_ci < part->chunk_count)
         {
             if (curctable[found_ci] == 0) curctable[found_ci] = chunk_start;
         }
     }
-    if (lastreconstruct >= 0)
+    if (firstfailrv == EXR_ERR_SUCCESS)
+    {
         memcpy (chunktable, curctable, chunkbytes);
+    }
+    else
+    {
+        for (int ci = 0; ci < part->chunk_count; ++ci)
+        {
+            if ( curctable[ci] != 0 )
+                chunktable[ci] = curctable[ci];
+        }
+    }
     ctxt->free_fn (curctable);
 
     return firstfailrv;