Compat: Fix defaultValue not applied when value==null/undefined

[marvinhagemeister]

This PR addresses an issue in preact/compat in regards to the handling of defaultValue. When both defaulValue and value are present, but the latter is null or undefined we would overwrite the correct value we set earlier with the wrong one. This lead to defaultValue effectively never being set.

Fixes #2954

[coveralls]

Coverage remained the same at 99.441% when pulling e0842e8 on compat-default-value into 5044515 on master.

[github-actions]

Size Change: +33 B (0%)

Total Size: 42.1 kB

Filename	Size	Change
compat/dist/compat.js	3.46 kB	+12 B (0%)
compat/dist/compat.module.js	3.48 kB	+10 B (0%)
compat/dist/compat.umd.js	3.52 kB	+11 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
debug/dist/debug.js	2.99 kB	0 B
debug/dist/debug.module.js	2.98 kB	0 B
debug/dist/debug.umd.js	3.07 kB	0 B
devtools/dist/devtools.js	232 B	0 B
devtools/dist/devtools.module.js	240 B	0 B
devtools/dist/devtools.umd.js	308 B	0 B
dist/preact.js	3.93 kB	0 B
dist/preact.min.js	3.98 kB	0 B
dist/preact.module.js	3.97 kB	0 B
dist/preact.umd.js	4.02 kB	0 B
hooks/dist/hooks.js	1.13 kB	0 B
hooks/dist/hooks.module.js	1.15 kB	0 B
hooks/dist/hooks.umd.js	1.2 kB	0 B
jsx-runtime/dist/jsxRuntime.js	327 B	0 B
jsx-runtime/dist/jsxRuntime.module.js	335 B	0 B
jsx-runtime/dist/jsxRuntime.umd.js	405 B	0 B
test-utils/dist/testUtils.js	437 B	0 B
test-utils/dist/testUtils.module.js	439 B	0 B
test-utils/dist/testUtils.umd.js	515 B	0 B

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