Editorial: Revert unintentional normative change for String.prototype…

….substr (tc39#2844)

`"a".substr(0, Infinity)` should return `"a"`, but tc39#2007 incorrectly changed the result to be `""`.

If we change `substr`'s algorithm to be more similar to
`String.prototype.substring` and `String.prototype.slice`, we can easily
fix this issue:

1. `min(intStart, size)` guarantees that `intStart` is now in `[0, size]`.
2. Clamping `intLength` guarantees it's also in `[0, size]`.

With these two changes, `intEnd = min(intStart + intLength, size)` is
now in range `[intStart, size]`, so we no longer have to check for
`intStart ≥ intEnd`, but instead can directly perform the `substring`
operation.

spec.html

@@ -47505,10 +47505,10 @@ <h1>String.prototype.substr ( _start_, _length_ )</h1>
           1. Let _intStart_ be ? ToIntegerOrInfinity(_start_).
           1. If _intStart_ is -&infin;, set _intStart_ to 0.
           1. Else if _intStart_ &lt; 0, set _intStart_ to max(_size_ + _intStart_, 0).
+          1. Else, set _intStart_ to min(_intStart_, _size_).
           1. If _length_ is *undefined*, let _intLength_ be _size_; otherwise let _intLength_ be ? ToIntegerOrInfinity(_length_).
-          1. If _intStart_ is +&infin;, _intLength_ &le; 0, or _intLength_ is +&infin;, return the empty String.
+          1. Set _intLength_ to the result of clamping _intLength_ between 0 and _size_.
           1. Let _intEnd_ be min(_intStart_ + _intLength_, _size_).
-          1. If _intStart_ &ge; _intEnd_, return the empty String.
           1. Return the substring of _S_ from _intStart_ to _intEnd_.
         </emu-alg>
         <emu-note>