Issues with space characters in .bdf's from the otf2bdf tool

Some .bdf's define a space like this:
```text
STARTCHAR 0020
ENCODING 32
SWIDTH 240 0
DWIDTH 2 0
BBX 0 0 0 0
BITMAP
ENDCHAR
```
But this causes `bdf2dict` to skip (omit) the glyph completely.

Need to make spaces defined like this process properly to an (empty) glyph of the correct width (eg the 'DWIDTH X' value)

This is currently worked around by manually modifying the relevant entries in source bdf's to look like:
```
STARTCHAR 0020
ENCODING 32
SWIDTH 240 0
DWIDTH 2 0
BBX 0 1 0 0
BITMAP
00
ENDCHAR
```