Can't render Nepali text using fallback font, "Bad font family"

[whitmer]

Hi, I'm running into some issues trying to get Prawn to render Nepali text, and I'm not sure where the issue might be, any help would be appreciated.

Using Prawn 2.2.2

pdf = Prawn::Document.new
pdf.font "lib/TimesNewRoman.ttf"
pdf.font_families.update({'MiedingerBook' => {
  normal: "lib/MiedingerBook.ttf" # https://github.com/CoughDrop/obf/blob/master/lib/MiedingerBook.ttf
}})
pdf.fallback_fonts = ['MiedingerBook']
pdf.text_box "भन्नुहोस्"
pdf.render_file("out/prawn.pdf")

When I run this I get:

Traceback (most recent call last):
       16: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/text/box.rb:134:in `render'
       15: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/text/formatted/box.rb:212:in `render'
       14: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/font.rb:215:in `save_font'
       13: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/text/formatted/box.rb:213:in `block in render'
       12: from /Users/me/.rvm/gems/ruby-2.6.1/gems/pdf-core-0.7.0/lib/pdf/core/text.rb:214:in `character_spacing'
       11: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/text/formatted/box.rb:214:in `block (2 levels) in render'
       10: from /Users/me/.rvm/gems/ruby-2.6.1/gems/pdf-core-0.7.0/lib/pdf/core/text.rb:190:in `text_rendering_mode'
        9: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/text/formatted/box.rb:219:in `block (3 levels) in render'
        8: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/font.rb:101:in `font_size'
        7: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/text/formatted/box.rb:226:in `block (4 levels) in render'
        6: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/text/formatted/wrap.rb:53:in `wrap'
        5: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/text/formatted/line_wrap.rb:47:in `wrap_line'
        4: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/text/formatted/line_wrap.rb:77:in `apply_font_settings_and_add_fragment_to_line'
        3: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/text/formatted/arranger.rb:166:in `apply_font_settings'
        2: from /Users/me/.rvm/gems/ruby-2.6.1/gems/pdf-core-0.7.0/lib/pdf/core/text.rb:214:in `character_spacing'
        1: from /Users/me/.rvm/gems/ruby-2.6.1/gems/prawn-2.2.2/lib/prawn/text/formatted/arranger.rb:168:in `block in apply_font_settings'
RuntimeError (Bad font family)

However if I set the font explicitly instead of using the fallback then the error goes away. I have tested this with multiple Nepali fonts and gotten the same result. However, the issue doesn't come up when using a Thai font as a fallback for Thai strings.