.show without arguments kills the bayeslite shell

[fsaad]

When entering ".show" without arguments, the bayeslite shell freaks out and terminates.

to reproduce:

fsaad@fsaad-xps:/Documents/pcp/crime/src$ bayeslite -m
added command ".register_bql_math_functions"
added command ".readtohtml"
added command ".nullify"
added command ".heatmap"
added command ".show"
added command ".ccstate"
added command ".histogram"
added command ".bar"
added command ".chainplot"
Welcome to the Bayeslite shell.
Type `.help' for help.
bayeslite> .show
usage: bayeslite [-h] [-f FILENAME] [-g GENERATOR] [-s] [--no-contour] [-m]
[--colorby COLORBY]
bql [bql ...]
bayeslite: error: too few arguments
fsaad@fsaad-xps:/Documents/pcp/crime/src$ <--- bayeslite exits here --->

[riastradh-probcomp]

Fixed in a823a0a.