Ensure mask buffer is properly freed

Author: JorjMcKie

src/extra.i

@@ -3504,10 +3504,11 @@ void JM_make_image_block(fz_stext_block *block, PyObject *block_dict)
 {
     fz_context* ctx = mupdf::internal_context_get();
     fz_image *image = block->u.i.image;
-    fz_buffer *buf = NULL, *freebuf = NULL;
+    fz_buffer *buf = NULL, *freebuf = NULL; *mask_buf = NULL;
     fz_compressed_buffer *buffer = fz_compressed_image_buffer(ctx, image);
     fz_var(buf);
     fz_var(freebuf);
+    fz_var(mask_buf);
     int n = fz_colorspace_n(ctx, image->colorspace);
     int w = image->w;
     int h = image->h;
@@ -3539,10 +3540,8 @@ void JM_make_image_block(fz_stext_block *block, PyObject *block_dict)
         } 
         bytes = JM_BinFromBuffer(buf);
         if (image->mask) {
-            fz_buffer *mask = fz_new_buffer_from_image_as_png(ctx, image->mask, fz_default_color_params);
+            mask_buf = fz_new_buffer_from_image_as_png(ctx, image->mask, fz_default_color_params);
             mask_bytes = JM_BinFromBuffer(mask);
-            fz_drop_buffer(ctx, mask);
-
         } else {
             mask_bytes = Py_BuildValue("s", NULL);
         }
@@ -3570,7 +3569,7 @@ void JM_make_image_block(fz_stext_block *block, PyObject *block_dict)
                         Py_BuildValue("n", PyBytes_Size(bytes)));
         DICT_SETITEM_DROP(block_dict, dictkey_image, bytes);
         DICT_SETITEMSTR_DROP(block_dict, "mask", mask_bytes);
-
+        fz_drop_buffer(ctx, mask_buf);
         fz_drop_buffer(ctx, freebuf);
     }
     fz_catch(ctx) {;}