Support empty parquet metadata files

[smcguire-cmu]

Supports parquet _metadata files with no row groups. Part of astronomy-commons/lsdb#867

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Before [ea9a91e]	After [baaf9c1]	Ratio	Benchmark (Parameter)
225±2ms	226±3ms	1.01	benchmarks.time_open_large_catalog
12.2±0.3ms	12.2±0.3ms	1	benchmarks.Suite.time_inner_pixel_alignment
36.3±0.8ms	36.2±0.5ms	1	benchmarks.Suite.time_pixel_tree_creation
35.1±0.2ms	35.0±0.2ms	1	benchmarks.time_open_midsize_catalog
227±2ms	226±0.6ms	1	benchmarks.time_small_cone_large_catalog
106±0.1ms	106±0.3ms	1	benchmarks.time_test_alignment_even_sky
1.03±0.02ms	1.03±0.05ms	1	benchmarks.time_test_cone_filter_multiple_order
363±0.9ms	360±2ms	0.99	benchmarks.Suite.time_outer_pixel_alignment

Click here to view all benchmarks.