force a make clean first

Change-Id: Icef93accc6953a4484707fb9da01a85963002a21
Resolves: coverity#706171 Untrusted value as argument

limit nBytesToRead to remaining size of file

also zero last byte of alloced block, seeing as the
block is size+1 and we only read size into it

Change-Id: I2729ec7bb9de20731531f32da864c572fa83ce58