Debugger: Fix removal of expression that ends with whitespace

* Start a debugging session
* Add an evaluated expression "(char*)foo "
* Delete the expression
* Press F10
* It reappears

Change-Id: I5c54ca6ab2f4be6c613880a2747e4aff653d15be
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

src/plugins/debugger/debuggerplugin.cpp

@@ -919,6 +919,7 @@ public slots:
             exp = removeObviousSideEffects(exp);
         else
             exp = fixCppExpression(exp);
+        exp = exp.trimmed();
         if (exp.isEmpty())
             return;
         currentEngine()->watchHandler()->watchVariable(exp);