Small fix for the "memory write -i filename" command -- if the user fails to specify the

Small fix for the "memory write -i filename" command -- if the user fails to specify the
number of bytes to write into the inferior process, the "default byte size" will be 1.
In that case, we want to copy the entire file into memory.  The code was looking for
a default byte size of 0 to indicate that the user had not provided a specific # of
bytes to copy; adjust that to 1 to match the actual default value.
<rdar://problem/18074973>

llvm-svn: 228067