Todo: Fix crash on MSVC when chars >0x7f are read

Change-Id: I919c1d795f846b9a16c4428f7d2cd91be7e04c75
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>

src/plugins/todo/cpptodoitemsscanner.cpp

@@ -96,9 +96,9 @@ void CppTodoItemsScanner::processDocument(CPlusPlus::Document::Ptr doc)
 
             const char *start = source.constData() + from;
             const char *end = source.constData() + to;
-            while (start != end && std::isspace(*start))
+            while (start != end && std::isspace((unsigned char)*start))
                 ++start;
-            while (start != end && std::isspace(*end))
+            while (start != end && std::isspace((unsigned char)*end))
                 --end;
             const int length = end - start + 1;
             if (length > 0) {