Preserve empty location for empty files

Without a region, error messages in exceptions are unable to print
a filename.

By retaining the location in a zero-length region and detecting this
when formatting the exception text it is possible to print the filename
and explicitly state that the file is completely empty.

Fixes #160

README.md

@@ -1943,6 +1943,8 @@ I appreciate the help of the contributors who introduced the great feature to th
   - Add missing include files
 - sneakypete81 (@sneakypete81)
   - Fix typo in error message
+- Oliver Kahrmann (@founderio)
+  - Fix missing filename in error message if parsed file is empty
 
 
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