Fix possible memory leak in runScript.c

This was reported by cppcheck over require's code:
require-ess/src/runScript.c:128:12: error: Common realloc mistake: 'line_raw' nulled but not freed upon failure [memleakOnRealloc]
      if ((line_raw = realloc(line_raw, line_raw_size *= 2)) == NULL)
           ^

Unfortunately realloc can return null, in that case if we use something
like
line_raw = realloc(line_raw, size);
The memory pointed by line_raw is lost.