Don't warn on python/prospector with no messages.
Don't warn on python/prospector with no messages.

When the python/prospector checker finds no issues in the file, the "messages" key is absent in the JSON output. Make sure we don't spew out a warning when that happens.
wezhang/vim-setup,wezhang/vim-setup,wezhang/vim-setup,wezhang/vim-setup,wezhang/vim-setup,wezhang/vim-setup