error handling for showPctFull='true' when metric='all'

[mhweber]

Requesting all metrics in StreamCatTools

df <- sc_get_data(comid='179', aoi='ws', metric='all')

Gives this appropriate warning message

Using metric='all' with a large aoi may take a considerable amount of time to return results - request may timeout if multiple AOIs are requested

However adding showPctFull='true'

df <- sc_get_data(comid='179', aoi='ws', metric='all',showPctFull='true')

Gives the warning plus an unhelpful HTTP 555 error message

Using metric='all' with a large aoi may take a considerable amount of time to return results - request may timeout if multiple AOIs are requested
An error occurred during req_perform(); the service may be down or function parameters may be mis-specified: HTTP 555.