Blank ERROR: when max download limit reached (with fix)

When the --max-download limit is reached, the code raises a MaxDownloadsReached exception, which leads to a blank ERROR: line on the standard error console, with no additional error message.  This is uninformative.

Reaching the maximum number of downloads is not an error.  The program is functioning as intended.

I'm submitting a pull request here which should silence the ERROR: message for runs that reach the max-downloads limit.  The appropriate informational message that this condition exists is still printed.