Better error for invalid DESCRIPTION

[gaborcsardi]

User had a blank line after the Suggests entry in his DESCRIPTION file here: https://github.com/sbgraves237/Ecfun/blob/996afae57efcd56e1587f57a3b8fe9fe062519ba/DESCRIPTION#L14, and that caused remotes::dev_package_deps() to die with this obscure error:

Error in data.frame(package = deps, installed = inst_ver, available =
cran_ver,  :
   row names contain missing values
Calls: saveRDS ... <Anonymous> -> package_deps -> structure -> data.frame

For comparison, the remotes::install_local() function ignores the blank line, R CMD INSTALL fails with error

Error: contains a blank line

(but doesn't say which file contains it!).