Properly unset href on nullish value

[marvinhagemeister]

Fixes #1943

[coveralls]

Coverage increased (+0.8%) to 99.802% when pulling 0ba17ed on unset-href into 9fc5910 on master.

[github-actions]

Size Change: +20 B (0%)

Total Size: 40.5 kB

Filename	Size	Change
dist/preact.js	3.97 kB	+6 B (0%)
dist/preact.min.js	4 kB	+5 B (0%)
dist/preact.module.js	3.99 kB	+5 B (0%)
dist/preact.umd.js	4.03 kB	+4 B (0%)

ℹ️ View Unchanged

Filename	Size	Change
compat/dist/compat.js	3.26 kB	0 B
compat/dist/compat.module.js	3.28 kB	0 B
compat/dist/compat.umd.js	3.31 kB	0 B
debug/dist/debug.js	3.06 kB	0 B
debug/dist/debug.module.js	3.06 kB	0 B
debug/dist/debug.umd.js	3.15 kB	0 B
devtools/dist/devtools.js	185 B	0 B
devtools/dist/devtools.module.js	195 B	0 B
devtools/dist/devtools.umd.js	260 B	0 B
hooks/dist/hooks.js	1.09 kB	0 B
hooks/dist/hooks.module.js	1.11 kB	0 B
hooks/dist/hooks.umd.js	1.17 kB	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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