Bad regex causes code to fail

When using these options:
`{
compact: false,
identifierNamesGenerator: 'mangled',
stringArray: true,
stringArrayEncoding: 'base64'
}`

This code:

`main();
function main() {
alert("Hello world!")
}`

Obfuscates as the following code, which fails due to the regex /=+$/:

`var a = ['SGVsbG8gd29ybGQh'];
(function (c, d) {
var e = function (f) {
while (--f) {
c['push'](c['shift']());
}
};
e(++d);
}(a, 0x6f));
var b = function (c, d) {
c = c - 0x0;
var e = a[c];
if (b['yZthrT'] === undefined) {
(function () {
var f = function () {
var g;
try {
g = Function('return\x20(function()\x20' + '{}.constructor(\x22return\x20this\x22)(\x20)' + ');')();
} catch (h) {
g = window;
}
return g;
};
var i = f();
var j = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
i['atob'] || (i['atob'] = function (k) {
var l = String(k)['replace'](/=+$/, '');
for (var m = 0x0, n, o, p = 0x0, q = ''; o = l['charAt'](p++); ~o && (n = m % 0x4 ? n * 0x40 + o : o, m++ % 0x4) ? q += String['fromCharCode'](0xff & n >> (-0x2 * m & 0x6)) : 0x0) {
o = j['indexOf'](o);
}
return q;
});
}());
b['aypUXW'] = function (r) {
var s = atob(r);
var t = [];
for (var u = 0x0, v = s['length']; u < v; u++) {
t += '%' + ('00' + s['charCodeAt'](u)['toString'](0x10))['slice'](-0x2);
}
return decodeURIComponent(t);
};
b['EhRyAC'] = {};
b['yZthrT'] = !![];
}
var w = b['EhRyAC'][c];
if (w === undefined) {
e = b['aypUXW'](e);
b['EhRyAC'][c] = e;
} else {
e = w;
}
return e;
};
main();
function main() {
alert(b('0x0'));
}`

Reproduce the failure with the listed obfuscation options and sample JavaScript, then inspect the generated base64 decoder around the ` /=+$/ ` expression. Confirm the generated output runs successfully after the regex issue is addressed, using the supplied example as the completion check.

Written by the indexing model from the issue text.