[lldb] Fix SocketTest.DomainGetConnectURI on macOS by stripping more zeroes from getpeername result

Apparently macOS is padding the name result with several padding zeroes at
the end. Just strip them all to pretend it's a C-string.

Thanks to Pavel for suggesting this fix.

lldb/source/Host/posix/DomainSocket.cpp

@@ -143,8 +143,7 @@ std::string DomainSocket::GetSocketName() const {
   llvm::StringRef name(saddr_un.sun_path + GetNameOffset(),
                        sock_addr_len - offsetof(struct sockaddr_un, sun_path) -
                            GetNameOffset());
-  if (name.back() == '\0')
-    name = name.drop_back();
+  name = name.drop_while([](char c) { return c == '\0'; });
 
   return name.str();
 }