Graceful error handling when loading malformed data.

[pateljm]

When loading data using the COPY command if the input file is malformed, then we abort printing the following message:

libc++abi.dylib: terminating with uncaught exception of type quickstep::TextScanFormatError: TextScanFormatError: Malformed data encountered during text scan (Row has too many fields)

Handle such errors gracefully by warning the user and aborting the load, and not crashing the system.

[cramja]

The message that is generated comes from a failed globbing syscall. I will make a PR to make this more understandable.

    The glob() function shall fail and return the corresponding value if:
    GLOB_ABORTED
        The scan was stopped because GLOB_ERR was set or (*errfunc()) returned non-zero.
    GLOB_NOMATCH
        The pattern does not match any existing pathname, and GLOB_NOCHECK was not set in flags.
    GLOB_NOSPACE
        An attempt to allocate memory failed.

From glob.h

The issue which @pateljm you are running into I think requires some reworking of how the work orders talk to each other going up the DAG. I will submit a small PR to outright crash the system (which is better than inexplicably hanging as it does for me now) and then work on correcting the no-file case more gracefully.