(This is behavior, not crash issue, as the latter is when there is no traceback.)

The editor code was added 3 years ago in #37929, PR-15452, to correct using the configured char width after font and window size changes make that invalid.  It is based on 
https://www.tcl.tk/man/tcl8.6/TkCmd/text.html#M21
"If the font does not have a uniform width then the width of the character “0” [zero] is used in translating from character units to screen units."  The implies that said char width is non-zero.  It would seem like a font bug if not.  This is first report I know of where width is 0.

The current code implements this as
       zero_char_width = \
            Font(text, font=text.cget('font')).measure('0')

Matej, what OS and font gives this error?  Please run the following, also uploaded, with the offending font, replacing the name I used.

import tkinter as tk
from tkinter.font import Font
r = tk.Tk()
t = tk.Text(r, font=('Source Code Pro', 10, 'normal'))
t.pack()
s = '0oO !*}'
t.insert('1.0', s) # Only to check that all above is valid.
for c in s:
    print(Font(t, font=t['font']).measure(c))

For fixed 10 pitch Source Code Pro, all widths are 8.
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We could, of course, catch ZeroDivisionError, but when then?  This is why I want to know what OS, font, and a test with multiple characters.

On possibility is to check whenever font is set, but still, what then?