JSStringGetUTF8CString writes beyond the provided buffer size

[robert-jenner]

44cd5f3

JSStringGetUTF8CString writes beyond the provided buffer size
rdar://122388595

Reviewed by Yusuke Suzuki.

U8_APPEND only checks the capacity in the non-ascii case,
so we should make sure we always check.

* Source/WTF/wtf/unicode/UTF8Conversion.cpp:
(WTF::Unicode::convertLatin1ToUTF8):
(WTF::Unicode::convertUTF16ToUTF8):
* Source/WebCore/dom/TextEncoder.cpp:
(WebCore::TextEncoder::encodeInto):

Originally-landed-as: 272448.625@safari-7618-branch (800c12a28dea). rdar://128091153

44cd5f3

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✅ 🧪 webkitperl	❌ 🧪 ios-wk2	❌ 🧪 api-mac	❌ 🧪 api-wpe
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❌ 🛠 🧪 jsc-arm64	❌ 🛠 tv	❌ 🧪 mac-AS-debug-wk2	❌ 🧪 gtk-wk2
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[webkit-early-warning-system]

EWS run on current version of this PR (hash 44cd5f3)

Misc	iOS, tvOS & watchOS	macOS	Linux	Windows
✅ 🧪 style	❌ 🛠 ios	❌ 🛠 mac	❌ 🛠 wpe	❌ 🛠 wincairo
	❌ 🛠 ios-sim	❌ 🛠 mac-AS-debug	❌ 🧪 wpe-wk2
✅ 🧪 webkitperl	❌ 🧪 ios-wk2	❌ 🧪 api-mac	❌ 🧪 api-wpe
	❌ 🧪 ios-wk2-wpt	❌ 🧪 mac-wk1	⏳ 🛠 wpe-skia
❌ 🛠 🧪 jsc	❌ 🧪 api-ios	❌ 🧪 mac-wk2	❌ 🛠 gtk
❌ 🛠 🧪 jsc-arm64	❌ 🛠 tv	❌ 🧪 mac-AS-debug-wk2	❌ 🧪 gtk-wk2
	❌ 🛠 tv-sim	❌ 🧪 mac-wk2-stress	❌ 🧪 api-gtk
	❌ 🛠 watch		❌ 🛠 jsc-armv7
	❌ 🛠 watch-sim		❌ 🧪 jsc-armv7-tests