[lldb] Start a new line for the next output if there are no symbols in the current symtab

Summary:
If there is no newline the "lldb" prompt could be on the wrong line. To reproduce the missing newline you can do 'image dump smytab' on any binary.

Previously

Symtab, file = D:\upstream\build\Debug\bin\clang-diff.exe, num_symbols = 0(lldb)

Now

Symtab, file = D:\upstream\build\Debug\bin\clang-diff.exe, num_symbols = 0
(lldb)

Reviewers: zturner, aleksandr.urakov, lldb-commits

Subscribers: abidh

Differential Revision: https://reviews.llvm.org/D52627

llvm-svn: 343497