Return early if there's nothing to lint

[MichaelChirico]

Accidentally linted a directory where everything was excluded, leading to an error from txtProgressBar():

Error in txtProgressBar(max = length(files), style = 3L) : 
  must have 'max' > 'min'

Better to just skip running anything if there's nothing to lint.

[codecov-commenter]

Codecov Report

Merging #2202 (ff9080c) into main (f8fab18) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head ff9080c differs from pull request most recent head 2b6f59a. Consider uploading reports for the commit 2b6f59a to get more accurate results

@@           Coverage Diff           @@
##             main    #2202   +/-   ##
=======================================
  Coverage   99.65%   99.65%           
=======================================
  Files         113      113           
  Lines        5155     5159    +4     
=======================================
+ Hits         5137     5141    +4     
  Misses         18       18           

Files Changed	Coverage Δ
R/lint.R	98.90% <100.00%> (+0.01%)	⬆️

[IndrajeetPatil]

Just need to update NEWS here. Othewise, LGTM.

[MichaelChirico]

Nothing to update. This is really a regression after #2133. So it's a dev-only improvement.