Fix #108243: Crash when save before close with modified image

A mistake in the recent API refactor for the buffer sharing.

Pull Request: https://projects.blender.org/blender/blender/pulls/108259

source/blender/blenkernel/intern/image.cc

@@ -1352,8 +1352,8 @@ static bool image_memorypack_imbuf(
   ImagePackedFile *imapf;
   PackedFile *pf = MEM_cnew<PackedFile>("PackedFile");
 
-  pf->data = IMB_steal_encoded_buffer(ibuf);
   pf->size = ibuf->encoded_size;
+  pf->data = IMB_steal_encoded_buffer(ibuf);
 
   imapf = static_cast<ImagePackedFile *>(MEM_mallocN(sizeof(ImagePackedFile), "Image PackedFile"));
   STRNCPY(imapf->filepath, filepath);

source/blender/imbuf/IMB_imbuf.h

@@ -179,7 +179,8 @@ void IMB_make_writable_byte_buffer(struct ImBuf *ibuf);
 void IMB_make_writable_float_buffer(struct ImBuf *ibuf);
 
 /* Steal the buffer data pointer: the ImBuf is no longer an owner of this data.
- * NOTE: If the ImBuf does not own the data the behavior is undefined. */
+ * NOTE: If the ImBuf does not own the data the behavior is undefined.
+ * NOTE: Stealing encoded buffer resets the encoded size. */
 uint8_t *IMB_steal_byte_buffer(struct ImBuf *ibuf);
 float *IMB_steal_float_buffer(struct ImBuf *ibuf);
 uint8_t *IMB_steal_encoded_buffer(struct ImBuf *ibuf);

source/blender/imbuf/intern/allocimbuf.cc

@@ -100,6 +100,7 @@ bool imb_alloc_buffer(
   }
 
   buffer.ownership = IB_TAKE_OWNERSHIP;
+  buffer.implicit_sharing = nullptr;
 
   return true;
 }
@@ -416,6 +417,7 @@ bool imb_enlargeencodedbufferImBuf(ImBuf *ibuf)
 
   imb_free_buffer(ibuf->encoded_buffer);
 
+  ibuf->encoded_buffer = new_buffer;
   ibuf->encoded_buffer_size = newsize;
   ibuf->flags |= IB_mem;