gen-verilog: nested struct field after part-select emits glued identifier — fifo.v is invalid Verilog on master

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Live codegen regression on master (appeared with the gold-ring compiler merge, absorbed silently by the warning-only lint gate 40 minutes after the '32/32' claim of #2216): specs/fpga/fifo.t27 'return state.flags.empty;' emits 'is_empty = state[96 +: 4]_empty;' — an identifier fragment glued onto a part-select. 6 occurrences in fifo.v; yosys: 'fifo.v:237: ERROR: syntax error, unexpected TOK_ID'. Reproduced from the run's own digest-verified artifact. Once the lint gate fails honestly (see the vacuous-greens fix), fpga-lint will be red until this is fixed. Refs #2239.