improve compliance with LESS's strictMath
improve compliance with LESS's strictMath

BS3 commits: 88d8cd90e2cef123b9389187e0d5acd1c9f1026d

2947721120/googlebt4,mozillo/todc-bootstrap,up2vs/todc-bootstrap,2947721120/todc-bootstrap,todc/todc-bootstrap,ztx1491/todc-bootstrap,todc/todc-bootstrap,aaroncnhk/todc-bootstrap,todc/todc-bootstrap