font-patcher: Check if glyph source is available

[why]
When users just download the script (and not the source glyphs) the
script fails with an obscure error message.

[how]
Check if the glyphdir exists at all. If not give a hint to download the
glyphs.

Check if the individual glyph font exists and is readable. Bail out if
not.

[note]
Cherry picked, was part of ryanoasis#741

Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>

font-patcher

@@ -218,13 +218,23 @@ class font_patcher:
  PreviousSymbolFilename = ""
  symfont = None
 
+ if not os.path.isdir(self.args.glyphdir):
+ sys.exit("{}: Can not find symbol glyph directory {} "
+ "(probably you need to download the src/glyphs/ directory?)".format(projectName, self.args.glyphdir))
+
  for patch in self.patch_set:
  if patch['Enabled']:
  if PreviousSymbolFilename != patch['Filename']:
  # We have a new symbol font, so close the previous one if it exists
  if symfont:
  symfont.close()
  symfont = None
+ if not os.path.isfile(self.args.glyphdir + patch['Filename']):
+ sys.exit("{}: Can not find symbol source for '{}'\n{:>{}} (i.e. {})".format(
+ projectName, patch['Name'], '', len(projectName), self.args.glyphdir + patch['Filename']))
+ if not os.access(self.args.glyphdir + patch['Filename'], os.R_OK):
+ sys.exit("{}: Can not open symbol source for '{}'\n{:>{}} (i.e. {})".format(
+ projectName, patch['Name'], '', len(projectName), self.args.glyphdir + patch['Filename']))
  symfont = fontforge.open(os.path.join(self.args.glyphdir, patch['Filename']))
 
  # Match the symbol font size to the source font size