Here is a GDB script to fix it (tested on GNU/Linux only):
tbreak _ZN3App9initMediaEv
commands
set {char}_ZN3App9msgRadiusEv=0xB8
set {int}(_ZN3App9msgRadiusEv+1)=3
set {char}(_ZN3App9msgRadiusEv+5)=0xC3
set {char}_Z25replaceStringWithEntitiesRK13QLatin1String5QCharR7QStringP5QListI12EntityInTextEb = 0xC3
end
run
detach
quit
Run it like this, assuming it is saved to msgRadius.gdb and Telegram is /usr/bin/telegram-desktop:
$ gdb -x msgRadius.gdb /usr/bin/telegram-desktop
This replaces the start of App::msgRadius with
mov $0x3, %eax
retq
In C++, that is return 3;
Explanation: 0xB8 means mov a number to %eax, 3 is the border radius, and 0xC3 is retq.
The first instruction in replaceStringWithEntities gets replacemed by a retq, bypassing it.
I'd like to note that this is forked (uncredited) from something I made: telegramdesktop/tdesktop#2235 (comment)