Avoid panic from `DumpRegister` in circuit display

[swernli]

This avoids a panic on empty state that can happen when DumpRegister is called on an empty state vector, such as when generating a circuit without any underlying quantum simulation.

[github-actions[bot]]

Benchmark for 5b807cc

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| Test | Base | PR | % | |------|--------------|------------------|---| | Array append evaluation | **325.9±1.48µs** | 328.1±2.36µs | **+0.68%** | | Array literal evaluation | 186.8±1.15µs | **176.4±1.00µs** | **-5.57%** | | Array update evaluation | 409.4±2.09µs | 409.7±2.43µs | +0.07% | | Core + Standard library compilation | 19.0±0.33ms | 19.3±1.05ms | +1.58% | | Deutsch-Jozsa evaluation | **5.0±0.04ms** | 5.1±0.04ms | **+2.00%** | | Large file parity evaluation | 33.9±0.11ms | 33.9±0.26ms | 0.00% | | Large input file compilation | 12.8±0.30ms | 13.0±0.29ms | +1.56% | | Large input file compilation (interpreter) | 47.5±0.82ms | 47.7±0.93ms | +0.42% | | Large nested iteration | **32.4±0.47ms** | 33.0±1.00ms | **+1.85%** | | Perform Runtime Capabilities Analysis (RCA) on Deutsch-Jozsa sample | 1570.4±39.74µs | 1561.9±57.08µs | -0.54% | | Perform Runtime Capabilities Analysis (RCA) on large file sample | 7.9±0.09ms | **7.8±0.18ms** | **-1.27%** | | Perform Runtime Capabilities Analysis (RCA) on teleport sample | 1435.5±36.88µs | 1420.0±46.31µs | -1.08% | | Perform Runtime Capabilities Analysis (RCA) on the core and std libraries | 28.3±0.30ms | **28.1±0.15ms** | **-0.71%** | | Teleport evaluation | 88.3±5.33µs | 89.1±3.70µs | +0.91% |