MOBI Input: When extracting images, ignore records that are known as non images faster

src/calibre/ebooks/mobi/reader.py

@@ -933,6 +933,9 @@ class MobiReader(object):
                 continue
             processed_records.append(i)
             data  = self.sections[i][0]
+            if data[:4] in (b'FLIS', b'FCIS', b'SRCS', b'\xe9\x8e\r\n'):
+                # A FLIS, FCIS, SRCS or EOF record, ignore
+                continue
             buf = cStringIO.StringIO(data)
             image_index += 1
             try: