TTF files leave atlas 0_0 unused

Discovered while testing MC-278245.

The bug

When the game stitches font characters to the font atlas, when using a ttf font, it will always start from 1_0, leaving 0_0 unused except for the missing glyph.

How to reproduce

1. Download and apply the resource pack from MC-278245

2. /tellraw @p {"text": "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789", "font": "seven"}

3. F3+S
4. Inspect the files minecraft_seven_0_0 and minecraft_seven_1_0

Expected results

All the characters would be part of minecraft_seven_0_0 as there's more than enough room for them. minecraft_seven_1_0 would not exist.

Actual results

minecraft_seven_1_0 does exist, containing all of the characters instead of minecraft_seven_0_0 doing that job.