[lldb-mi] Fix assignment operator in CMIUtilString
[lldb-mi] Fix assignment operator in CMIUtilString

Fix assignment operator in CMIUtilString to not crash the debugger if it
is passed a NULL pointer, which can happen in code like the following:

    SBValue val;
    CMIUtilString s;
    //...
    s = val.GetSummary();

Patch from evgeny.leviant@gmail.com
Reviewed by: clayborg, ki.stfu
Subscribers: lldb-commits
Differential Revision: http://reviews.llvm.org/D13094


git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@248597 91177308-0d34-0410-b5e6-96231b3b80d8

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