Fix error in filetype check.

Error also reported in #24.
test: Modularize the checks for invalid and valid filetypes.
[version] Bumped version from 0.4.4 to 0.4.5.
Merge branch 'release/0.4.5'

* release/0.4.5:
  [version] Bumped version from 0.4.4 to 0.4.5.
  test: Modularize the checks for invalid and valid filetypes.
  Fix error in filetype check.