Merge pull request #22 from matt-land/fix-variable-reference

fix for #21, always create reference

Author: FoamyGuy

adafruit_bitmapsaver.py

@@ -1,4 +1,5 @@
 # SPDX-FileCopyrightText: 2019 Dave Astels for Adafruit Industries
+# SPDX-FileCopyrightText: 2022 Matt Land
 #
 # SPDX-License-Identifier: MIT
 
@@ -10,7 +11,7 @@
 Make a screenshot (the contents of a displayio.Display) and save in a BMP file.
 
 
-* Author(s): Dave Astels
+* Author(s): Dave Astels, Matt Land
 
 Implementation Notes
 --------------------
@@ -79,6 +80,7 @@ def _write_pixels(output_file, pixel_source, palette):
     saving_bitmap = isinstance(pixel_source, Bitmap)
     width, height = _rotated_height_and_width(pixel_source)
     row_buffer = bytearray(_bytes_per_row(width))
+    result_buffer = False
     for y in range(height, 0, -1):
         buffer_index = 0
         if saving_bitmap:
@@ -98,8 +100,9 @@ def _write_pixels(output_file, pixel_source, palette):
                     row_buffer[buffer_index] = b & 0xFF
                     buffer_index += 1
         output_file.write(row_buffer)
-        for i in range(width * 2):
-            result_buffer[i] = 0
+        if result_buffer:
+            for i in range(width * 2):
+                result_buffer[i] = 0
         gc.collect()