fix(@angular/build): treat empty browsers array as undefined in unit-… #2816

Job	Run time
build-e2e-windows	22s
build	20s
lint	1m 57s
publish-snapshots	0s
test	0s
Browser Compatibility Tests	0s
e2e-package-managers	0s
e2e	0s
e2e-snapshots	0s
e2e-windows	0s
	2m 39s

Provide feedback