optimize: skip images with unusually small dimensions

They're unlikely to be handled well by our recompressors. It seems
that JBIG2 cannot handle very small widths.

Fixes #732

src/ocrmypdf/optimize.py

@@ -76,6 +76,9 @@ def extract_image_filter(
     if image.Length < 100:
         log.debug(f"Skipping small image, xref {xref}")
         return None
+    if image.Width < 8 or image.Height < 8:  # Issue 732
+        log.debug(f"Skipping oddly sized image, xref {xref}")
+        return None
 
     pim = PdfImage(image)