ClangTools: Reflect state of fixits

...in the fixit column to avoid confusion.

As a side effect, add some error handling.

Change-Id: Ia30e9c9782f3c8021aedd2be7c682853a26d3f39
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>

src/plugins/texteditor/refactoringchanges.h

@@ -79,7 +79,7 @@ public:
     void appendIndentRange(const Range &range);
     void appendReindentRange(const Range &range);
     void setOpenEditor(bool activate = false, int pos = -1);
-    void apply();
+    bool apply();
 
 protected:
     // users may only get const access to RefactoringFiles created through