Change CommandObjectTargetSymbolsAdd to require that a target exists; fixes crash of the form
Change CommandObjectTargetSymbolsAdd to require that a target exists;
fixes crash of the form

% lldb
(lldb) target symbols add /tmp/symbols.dSYM
(lldb) Killed: 9

<rdar://problem/13139481> 


git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@174267 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb