David Soria Parra <davidsp@fb.com> [Thu, 23 Jan 2014 19:08:26 +0100] rev 20316
parsers: fix 'unsigned expression is always true' warning (issue4142)
On Mac OS gcc-llvm throws an -Wtautological-compare warning because flen
is defined as an unsigned integer, therefore flen < 0 is always true.