Wrap frozen keys fix in try-catch not to break other WeakMap polyfills implementations

[eugef]

Other WeakMap polyfills throw an error if frozen object is being passed as a key.
So we simply ignore the error that this check produces.

This could happen if another polyfill was already executed on the page.

[eugef]

@zloirock could you review the PR?

[Jessidhia]

If there is a WeakMap polyfill that will crash when receiving a frozen object, then the bad polyfill should get overridden by core-js, instead of crashing (or being skipped, like this PR does).

Something like function isBad () { try { return new $WeakMap().set((Object.freeze || Object)(tmp), 7).get(tmp) != 7 } catch (e) { return true } } if (isBad()) { ... } might be more appropriate.

[eugef]

@Kovensky you are right, but unfortunately it is not always possible to do that.
And my PR just allows core-js to be more friendly to other code that can be already used on the page.

[zloirock]

I agree with @Kovensky. I'll add something for that.