premature use of startsWith in r75110

Hugh Parsonage writes:

In r75110 at line 1846 in src/library/tools/R/check.R the following
line was changed

- if(length(grep("^Found the defunct/removed function", out8)))
+ if(any(startsWith(out8, "Found the defunct/removed function")))

However, if `out8` is NULL at this point (which is plausible), the
original returns FALSE, but the second returns an error. Recommend

+ if(!is.null(out8) && any(startsWith(out8, "Found the defunct/removed
function")))

Best,

HP