Revive the error message from "process load" and SBProcess::LoadImage.

IsPointedCString has problems with ValueObjects of type eTypeHostAddress.  We should
figure out the right thing to do in that case, but the test is silly here because we're
reading a type we've defined, so we know it is a const char *, and if the memory is good, 
we won't be able to read any characters, when we do ReadPointedString.

<rdar://problem/26612812>

llvm-svn: 272087