Check fread's return value in tool/server.cc.

Some compilers complain and it's worth checking. Maybe the file changed in size
between ftell and fread.

Change-Id: I7898b8517556ec6899bd6e8866ba3d1cd7efd5f4
Reviewed-on: https://boringssl-review.googlesource.com/5763
Reviewed-by: Adam Langley <agl@google.com>
1 file changed