Fix TypeError with empty axes in FFT functions #899

Job	Run time
build_linux (3.12)	3m 24s
build_windows (3.10)	9m 2s
build_linux (3.10)	4m 6s
build_windows (3.14)	7m 48s
build_windows (3.13)	7m 7s
build_windows (3.12)	8m 27s
build_windows (3.11)	7m 51s
build_linux (3.14)	3m 26s
build_linux (3.13)	3m 33s
build_linux (3.11)	3m 27s
test_linux (3.11, false, ubuntu-latest)	2m 0s
test_linux (3.12, false, ubuntu-latest)	2m 1s
test_linux (3.13, false, ubuntu-latest)	1m 43s
test_linux (3.10, false, ubuntu-latest)	2m 12s
test_linux (3.14, false, ubuntu-latest)	1m 49s
test_windows (3.14, false, windows-latest)	3m 19s
test_windows (3.12, false, windows-latest)	3m 30s
test_windows (3.13, false, windows-latest)	3m 21s
test_windows (3.11, false, windows-latest)	3m 23s
test_windows (3.10, false, windows-latest)	3m 44s
	1h 25m 13s

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