QUrl::addQueryItem(key, value) performs invalid escaping for values that contain a '+'

After the following call on a QUrl instance url:

url.addQueryItem("test", "plus+and space");

one would expect the resulting url instance to procude an encoded query like this:

...&test=plus%2Band%20space

Or, following the convention to encode spaces as '+' in encoded queries, one might expect that:

...&test=plus%2Band+space

However, the current QUrl implementation does none of the above. Instead, it generates:

...&test=plus+and%20space

This is wrong, and most web applications will decode that test parameter as "plus and space". So the QUrl::addQueryItem() method effectively converts all '+' characters to spaces.

Additional note: The method QUrl::toPercentEncoding() works correctly in this regard. So the following code:

url.addEncodedQueryItem("id", QUrl::toPercentEncoding("plus+and space"));

will produce a correct result:

...&test=plus%2Band%20space