Crash without error when patching custom Iosevka .ttc
#### 🗹 Requirements

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#### 🎯 Subject of the issue

Experienced behavior:
When trying to patch a custom build of Iosevka with the complete set of icons, the patcher eventually crashes with no error message. When patching on windows, it crashes when patching the 6th font in the `.ttc`. However, on WSL, it crashes when patching the 51st font (out of 54). The crash does not occur if I use the `--careful` flag, however this is not a desirable workaround.

#### 🔧 Steps to reproduce
The Iosevka build script I am using is as follows:
```toml
[buildPlans.iosevka-custom]
family = "Iosevka Custom"
spacing = "normal"
serifs = "slab"
export-glyph-names = false

[buildPlans.iosevka-custom.ligations]
enables = [
    "centre-ops",
    "arrow",
    "arrow2",
    "trig",
    "eqeq",
    "exeq",
    "ineq",
    "eqeqeq",
    "exeqeq",
    "exeqeqeq",
    "eqexeq",
    "ltgt-diamond",
    "ltgt-slash-tag",
    "brst",
    "plusplus",
    "kern-dotty",
    "kern-bars",
    "logic",
    "llgg",
    "llggeq",
    # "dot-as-operator",
    "bar-triggers-op-centering",
    "html-comment",
    "brace-bar",
    "brack-bar",
    "connected-underscore",
    "connected-number-sign",
    "connected-tilde-as-wave",
    "connected-hyphen-as-semi-dashed-line"
]

[buildPlans.iosevka-custom.variants]
inherits = "ss20"

[buildPlans.iosevka-custom.variants.design]
zero = "dotted"
asterisk = "penta-low"
caret = "high"
paren = "flat-arc"
ampersand = "lower-open"
at = "fourfold-solid-inner"
lig-ltgteq = "slanted"
question = "corner"

[collectPlans.iosevka-custom]
from = ["iosevka-custom"]
```
I've uploaded the `.ttc` for this font [here](https://drive.google.com/file/d/16WQeNqtQSiqaabQa2BASFiHSQwgh_jzD/view?usp=sharing).

On windows, I am patching the font with `fontforge.exe -lang py --script font-patcher iosevka-custom.ttc -c --mono -w`, and on WSL I am patching with `./font-patcher iosevka-custom.ttc -c --mono`.
