docs: clarify when the sequence init runs IteratorClose

Comment-only. The previous wording ("on either abrupt completion")
could be read as closing the iterator on any failure, including a
throw from next() itself. Spelled out the actual rule: conversion
failures and wrong-length pairs close the source iterator, while a
throw from the stepping (next(), or reading the result's done/value)
does not, because the ES iterator protocol marks the iterator done on
such a throw and IteratorClose is skipped for a done iterator.

Author: adrian-niculescu

NativeScript/runtime/URLSearchParamsImpl.cpp

@@ -424,8 +424,12 @@ bool MaterializeInnerSequence(v8::Local<v8::Context> context,
 // by the caller) and append each [name, value] pair. Covers Array, Map, Set,
 // another URLSearchParams and generators uniformly. A pair whose length is
 // not exactly 2 throws a TypeError; a name/value that cannot be coerced to a
-// string aborts with the JS exception left pending. On either abrupt
-// completion the source iterator is closed first (ES IteratorClose).
+// string aborts with the JS exception left pending. On either of those two
+// failures the source iterator is closed first (ES IteratorClose). A throw
+// from the stepping itself (next(), or reading the result's done/value)
+// intentionally does NOT close the iterator: the ES iterator protocol marks
+// the iterator done on such a throw (IteratorStepValue), and IteratorClose
+// is skipped for a done iterator, which is also how for..of behaves.
 bool BuildFromSequence(v8::Local<v8::Context> context,
                        v8::Local<v8::Object> object,
                        v8::Local<v8::Function> iterMethod,