[Command] Simplify the code and make it less error prone. NFCI.

Pointed out by Jim.

llvm-svn: 330047
diff --git a/lldb/source/Commands/CommandObjectExpression.cpp b/lldb/source/Commands/CommandObjectExpression.cpp
index 5e2810e..fc62b39 100644
--- a/lldb/source/Commands/CommandObjectExpression.cpp
+++ b/lldb/source/Commands/CommandObjectExpression.cpp
@@ -623,10 +623,7 @@
   if (expr == nullptr)
     expr = command;
 
-  Target *target = m_interpreter.GetExecutionContext().GetTargetPtr();
-  if (!target)
-    target = GetDummyTarget();
-
+  Target *target = GetSelectedOrDummyTarget();
   if (EvaluateExpression(expr, &(result.GetOutputStream()),
                          &(result.GetErrorStream()), &result)) {