BUG: fix handling of missing 'version' metadata field version #1944

Job	Run time
cygwin (3.9)	4m 17s
mypy	19s
homebrew (3.8)	5m 36s
homebrew (3.11)	4m 57s
msvc (3.11)	4m 12s
pyston (3.8)	2m 11s
test (ubuntu, 3.7)	2m 29s
test (ubuntu, 3.11)	2m 45s
test (macos, 3.7)	3m 16s
test (macos, 3.11)	4m 52s
test (windows, 3.7)	1m 30s
test (windows, 3.11)	2m 9s
test (ubuntu, pypy-3.9)	2m 26s
test (ubuntu, 3.8)	2m 40s
test (ubuntu, 3.9)	2m 35s
test (ubuntu, 3.10)	2m 49s
test (ubuntu, 3.12-dev)	3m 3s
test (ubuntu, 3.11, ~=0.63.3)	2m 26s
test (ubuntu, 3.11, ~=0.64.0)	2m 36s
test (ubuntu, 3.11, ~=1.0.0)	2m 12s
test (ubuntu, 3.11, ~=1.1.0)	2m 17s
test (ubuntu, 3.11, @git+https://github.com/mesonbuild/meson.git)	3m 10s
	1h 4m 47s

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