GH-59: Fix the cannot identify image file ... issue

 The issue was occurring because `arange` was going out of range because of the `duration + 1` operation on the metadata parsing step

Author: ArtyomVancyan

src/thumbnails/ffmpeg.py

@@ -12,8 +12,7 @@ class _FFMpeg:
     """This class is used to parse the metadata of a video file."""
 
     def __init__(self, filepath):
-        duration, self.size = self._parse_metadata(filepath)
-        self.duration = int(duration + 1)
+        self.duration, self.size = self._parse_metadata(filepath)
 
     @staticmethod
     def _parse_duration(stdout):

src/thumbnails/video.py

@@ -20,7 +20,7 @@ def arange(start, stop, step):
 
     def _generator():
         nonlocal start
-        while start < stop:
+        while start <= stop:
             yield start
             start += step