Web: prevent crash when using `InnerSizeWriter::request_inner_size()` #6254

Job	Run time
Check formatting	11s
Run cargo-deny on Android	22s
Check for typos	5s
Run cargo-deny on iOS	23s
Test stable Windows 64bit MSVC	2m 0s
Test stable Windows 32bit MSVC	2m 59s
Run cargo-deny on Linux	23s
Test stable Windows 64bit GNU	2m 15s
Run cargo-deny on macOS	26s
Test stable Windows 32bit GNU	2m 33s
Run cargo-deny on Redox OS	24s
Test stable Linux 32bit	1m 59s
Run cargo-deny on web	20s
Test stable Linux 64bit	1m 45s
Run cargo-deny on Windows	27s
Test stable X11	1m 28s
Test stable Wayland	1m 35s
Test stable Android	1m 12s
Test stable Redox OS	47s
Test stable macOS	1m 6s
Test stable iOS x86_64	52s
Test stable iOS Aarch64	53s
Test stable web	1m 5s
Test nightly Windows 64bit MSVC	2m 0s
Test nightly Windows 32bit MSVC	1m 51s
Test nightly Windows 64bit GNU	2m 2s
Test nightly Windows 32bit GNU	2m 11s
Test nightly Linux 32bit	2m 31s
Test nightly Linux 64bit	1m 34s
Test nightly X11	1m 30s
Test nightly Wayland	1m 39s
Test nightly Android	1m 0s
Test nightly Redox OS	27s
Test nightly macOS	56s
Test nightly iOS x86_64	1m 7s
Test nightly iOS Aarch64	1m 15s
Test nightly web	1m 3s
Test 1.70.0 Windows 64bit MSVC	1m 4s
Test 1.70.0 Windows 32bit MSVC	1m 8s
Test 1.70.0 Windows 64bit GNU	1m 23s
Test 1.70.0 Windows 32bit GNU	1m 23s
Test 1.70.0 Linux 32bit	1m 16s
Test 1.70.0 Linux 64bit	57s
Test 1.70.0 X11	55s
Test 1.70.0 Wayland	54s
Test 1.70.0 Redox OS	26s
Test 1.70.0 macOS	46s
Test 1.70.0 iOS x86_64	39s
Test 1.70.0 iOS Aarch64	43s
Test 1.70.0 web	59s
Test 1.70.0 Android	49s
Test nightly web Atomic	1m 21s
	1h 1m 19s

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