better error when attempting to add images directly (#1158)

kindlecomicconverter/comicarchive.py

@@ -20,12 +20,13 @@
 
 from functools import cached_property, lru_cache
 import os
+from pathlib import Path
 import platform
 import distro
 from subprocess import STDOUT, PIPE, CalledProcessError
 from xml.dom.minidom import parseString
 from xml.parsers.expat import ExpatError
-from .shared import subprocess_run
+from .shared import IMAGE_TYPES, subprocess_run
 
 EXTRACTION_ERROR = 'Failed to extract archive. Try extracting file outside of KCC.'
 SEVENZIP = '7zz' if platform.system() == 'Darwin' else '7z'
@@ -65,6 +66,9 @@ class ComicArchive:
     def extract(self, targetdir):
         if not os.path.isdir(targetdir):
             raise OSError('Target directory doesn\'t exist.')
+        
+        if Path(self.basename).suffix.lower() in IMAGE_TYPES:
+            raise UserWarning('Put images into folder and drag and drop folder into KCC window.')
 
         missing = []