font-patcher fails to patch InputMono [original-source.otf, does not exist]
#### 🎯 Subject of the issue

I encounter the following issue when trying to patch InputMono fonts:

```
λ ~/Downloads/Fonts/Input_Fonts/Input fontforge -script ./font-patcher --careful --complete  --progressbars --mono Input-Regular_\(InputMono-Regular\).ttf
Copyright (c) 2000-2021. See AUTHORS for Contributors.
 License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
 with many parts BSD <http://fontforge.org/license.html>. Please read LICENSE.
 Version: 20201107
 Based on sources from 2021-09-20 10:22 UTC-ML-D-GDK3.
 Based on source from git with hash: 5bbc0e0406fb04e9f9ae419cd1d8ed9864b18f7e
The glyph named Tcommaaccent is mapped to U+021A.
  But its name indicates it should be mapped to U+0162.
The glyph named Delta is mapped to U+0394.
  But its name indicates it should be mapped to U+2206.
The glyph named Omega is mapped to U+03A9.
  But its name indicates it should be mapped to U+2126.
The glyph named tcommaaccent is mapped to U+021B.
  But its name indicates it should be mapped to U+0163.
The glyph named mu is mapped to U+03BC.
  But its name indicates it should be mapped to U+00B5.
The requested file, original-source.otf, does not exist
Traceback (most recent call last):
  File "/home/david/Downloads/Fonts/Input_Fonts/Input/./font-patcher", line 929, in <module>
    main()
  File "/home/david/Downloads/Fonts/Input_Fonts/Input/./font-patcher", line 924, in main
    patcher.patch()
  File "/home/david/Downloads/Fonts/Input_Fonts/Input/./font-patcher", line 88, in patch
    symfont = fontforge.open(self.args.glyphdir + patch['Filename'])
OSError: Open failed
```

#### 🔧 Your Setup

Pop!_OS 21.04
Alacritty
zsh

