When SolveSpace tries to display an Unicode code point (e.g. U+EA00 )
that does not exist in the embedded vector font (unifont.hex.gz) it hangs
in an endless loop in
`const BitmapFont::Glyph &BitmapFont::GetGlyph(char32_t codepoint)`.
The reason is that the binary search through the text file unifont-8.0.01.hex
that does the "lazy loading" of glyphs does not end.
Here is a short excerpt from the file:
```
D7FE:00007FFE63866DF66DEE6DDE63DE7FFE7FFE61866FBE638E6FBE6F867FFE0000
D7FF:00007FFE63866DF66DEE6DDE63DE7FFE7FFE61866FBE638E6FBE6FBE7FFE0000
F900:0080108810881FF8100800007FFE00000FF008100FF00810042002447FFE0000
F901:00047FFE008010841FFE10841FFC10841FFC10840880050003000CC0703E0000
```
When searching for `0xEA00` after some iterations of the while loop
2450010bbf/src/resource.cpp (L567)
both `first` and `last` end up pointing to F900. After that on each
consecutive iteration of the loop `last` ends up pointing to the LF (0x0A)
just before F900
2450010bbf/src/resource.cpp (L585)
and then `mid` ends up back on F900 here
2450010bbf/src/resource.cpp (L570)
and this will repeat enlessly.
The solution is to do
```
first++;
```
here
2450010bbf/src/resource.cpp (L591),
which will make `first==last` and change whe while loop contition to `while(first < last) {` thiw will
allow the while loop to exit.
Tested with
- 0xEA00 - non existent, not found in 16 iterations.
- 0xF900 - exists but takes exactly 16 iterations of the binary search to finish
- 0x0000 - found in 16 iterations
- 0xFFFD - the replacement Unicode code point for non-existing glyphs. Also the end of the font.
- 0xFFFFF - a codepoint beyond the end, not found and does not cause an exception
The lazy parsing of the vector front was introduced here.
645c2d90acFixes#1150
e07b082eb8