C++: fixed completion in braceless statements following a control statement.

- Changed generator to generate:
- Changed AST::lastToken to return 1 if there is none
- Changed Bind.cpp to set the scope of the block following a control
  statement to extend upto (and not including) the first token after
  the block. So basically, including any whitespace after the control
  statement.

Reviewed-by: Roberto Raggi

src/libs/cplusplus/ASTPath.cpp

@@ -67,7 +67,9 @@ bool ASTPath::preVisit(AST *ast)
     unsigned firstToken = ast->firstToken();
     unsigned lastToken = ast->lastToken();
 
-    if (firstToken > 0 && lastToken > firstToken) {
+    if (firstToken > 0) {
+        Q_ASSERT(lastToken > firstToken);
+
         unsigned startLine, startColumn;
         getTokenStartPosition(firstToken, &startLine, &startColumn);