Fix TestGdbRemoteLibrariesSvr4Support

D62502 had a bug (visible only with D62503 reverted), where it would
error out if attempting to read a string from memory and the memory page
after the string happened to be unmapped.

This fixes the problem by checking for whether ReadMemory read *any*
bytes, instead of checking whether it returned an error. A greater
question is whether ReadMemory should even return an error if it read at
least one byte, but I'm leaving that for a separate patch.

llvm-svn: 364748

lldb/source/Plugins/Process/POSIX/NativeProcessELF.cpp

@@ -120,7 +120,7 @@ NativeProcessELF::ReadSVR4LibraryInfo(lldb::addr_t link_map_addr) {
   char name_buffer[PATH_MAX];
   error = ReadMemory(link_map.l_name, &name_buffer, sizeof(name_buffer),
                      bytes_read);
-  if (!error.Success())
+  if (bytes_read == 0)
     return error.ToError();
   name_buffer[PATH_MAX - 1] = '\0';
 
@@ -176,4 +176,4 @@ NativeProcessELF::GetLoadedSVR4Libraries() {
   return library_list;
 }
 
-} // namespace lldb_private
+} // namespace lldb_private