Open 2-pass logfile in binary mode for both reading and writing.
This fixes a regression on Windows introduced by r22769 in which the data read
from the file was not properly zero terminated. The file was read as text,
which caused the \r characters to be suppressed. Since the zero termination
happens at the end of the buffer, and there was one byte less read per line,
this caused the remaining space on the buffer to contain random data.
Originally committed as revision 23251 to svn://svn.ffmpeg.org/ffmpeg/trunk