fix an unsigned to signed comparison (an iterator to a size)
fix an unsigned to signed comparison (an iterator to a size)

satovey/heekscad,haiqiangwang/heekscad,haiqiangwang/heekscad,satovey/heekscad,Funcan/heekscad,Funcan/heekscad,haiqiangwang/heekscad,satovey/heekscad,Funcan/heekscad,Funcan/heekscad,satovey/heekscad,haiqiangwang/heekscad