Fix encoding detection and exception on empty files

The encoding detection code was trying to catch encoding-related
exceptions when the file is opened. This doesn't make sense, because
at this point no data has been read, therefore no encoding errors can be
detected. Instead, catch encoding-related exceptions when the file
contents are read.

Also avoid bailing out with `Exception('Unknown encoding')` on empty
files.

codespell_lib/_codespell.py

@@ -177,7 +177,7 @@ def open_with_chardet(self, filename):
         self.encdetector.reset()
         with codecs.open(filename, 'rb') as f:
             for line in f:
-                self.encdetector.feed(line)
+                self.encdet
                 if self.encdetector.done:
                     break
         self.encdetector.close()
@@ -200,30 +200,26 @@ def open_with_chardet(self, filename):
         return lines, encoding
 
     def open_with_internal(self, filename):
-        curr = 0
-        while True:
-            try:
-                f = codecs.open(filename, 'r', encoding=encodings[curr])
-            except UnicodeDecodeError:
-                if not self.quiet_level & QuietLevels.ENCODING:
-                    print("WARNING: Decoding file using encoding=%s failed: %s"
-                          % (encodings[curr], filename,), file=sys.stderr)
-                    try:
-                        print("WARNING: Trying next encoding %s"
-                              % encodings[curr + 1], file=sys.stderr)
-                    except IndexError:
-                        pass
-
-                curr += 1
-            else:
-                lines = f.readlines()
-                f.close()
-                break
-        if not lines:
+        encoding = None
+        first_try = True
+        for encoding in encodings:
+            if first_try:
+                first_try = False
+            elif not self.quiet_level & QuietLevels.ENCODING:
+                print("WARNING: Trying next encoding %s"
+                      % encoding, file=sys.stderr)
+            with codecs.open(filename, 'r', encoding=encoding) as f:
+                try:
+                    lines = f.readlines()
+                except UnicodeDecodeError:
+                    if not self.quiet_level & QuietLevels.ENCODING:
+                        print("WARNING: Decoding file using encoding=%s failed: %s"
+                              % (encoding, filename,), file=sys.stderr)
+                else:
+                    break
+        else:
             raise Exception('Unknown encoding')
 
-        encoding = encodings[curr]
-
         return lines, encoding
 
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