Update test_3780 to avoid tripping on non-text blocks.

The test extracts text and images from a page. It drops any images
that are not fully included within the mediabox. Accordingly the
test never sees any images, so works fine.

In a new MuPDF commit, when the CLIP flag is sent, images are
restricted to the clip region - i.e. they always fit within the
mediabox, hence we now have images appearing in the list.

The fix is to skip any non-text blocks in the test.

Author: robinwatts

tests/test_font.py

@@ -206,6 +206,8 @@ def test_3780():
                 #    print(f'    {n}: {v!r}')
                 for i, block in enumerate(d['blocks']):
                     print(f'block {i}:')
+                    if block['type'] != 0:
+                        continue
                     for j, line in enumerate(block['lines']):
                         print(f'    line {j}:')
                         for k, span in enumerate(line['spans']):