NI PCI 6733 must have at least 2 instructions

[philipstarkey]

Original report (archived issue) by Philip Starkey (Bitbucket: pstarkey, GitHub: philipstarkey).

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If the NI PCI 6733 has less than 2 instructions (2 samples) in the HDF5 table, then the DAQmx library will raise an exception when programming the device. We should catch this error at compilation time, rather than at programming time, and display a more useful error message.

See: https://bitbucket-archive.labscriptsuite.org/#!/labscript_suite/labscript/issues/17/while-setting-values-for-the-ni-pic-6733 (labscript-suite/labscript#17)

[philipstarkey]

Original comment by Philip Starkey (Bitbucket: pstarkey, GitHub: philipstarkey).

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Note: Need to ensure that any check we add does not affect the ability to compile a connection table